Metal heater

ABSTRACT

The present invention aims to provide a metal heater that hardly causes dispersion in the temperature of a semiconductor wafer or the like upon heating, and heats it quickly without causing warping and sagging in its metal plate. The present invention provides a metal heater which includes metal plates and a heating element, wherein the number of said metal plates is a plural number, the heating element is sandwiched between the metal plates, and the thickness of a metal plate on a heating face side is the same as or larger than the thickness of a metal plate on a side opposite to said heating face side.

TECHNICAL FIELD

The present invention relates to a metal heater that is mainly used inthe semiconductor industry and optical industry.

BACKGROUND ART

With respect to an etching device, and a semiconductorproducing/examining device including a chemical vapor deposition deviceor the like, metal heaters having substrates of a metal material such asstainless steel have been used.

FIG. 4 is a cross-sectional view that schematically shows a metal heaterhaving a structure that has been conventionally used.

In this metal heater 450, a heater 453 in which a nichrome wire 452 issandwiched between silicon rubbers 461 is provided to an aluminum plate451 having a thickness of 15 mm.

SUMMARY OF THE INVENTION

However, metal heaters with such structures have the following problems.

Metal plates to be used for the metal heaters are needed to have athickness to a certain extent. It is because if the metal plates arethin, the rigidity are low and the metal plates are warped and saggedsince the metal plates are pushed from the surrounding because ofthermal expansion attributed to heating or there is a difference ofthermal expansion coefficients between supporting cases and metalplates.

If such warping, sagging and the like occurs in the metal plates, asemiconductor wafer placed on the metal plates cannot be heated evenly,so that a dispersion of temperature or a damage in the semiconductorwafer is generated in some cases.

However, if the metal plates are made thick, the heat capacity of themetal plates is increased, and in the case of heating or cooling anobject to be heated, the temperature of the heating faces of the metalplates cannot promptly follow the change of the voltage or the electriccurrent applied to the heating elements, and there has been a problemthat temperature control becomes difficult.

Further, there has been a problem that it takes a long time (a longrecovery time) to recover the previous temperature of the heating faceand productivity reduces in the case a semiconductor wafer is placed onthe metal plate and the temperature of the heating face of the metalplate abruptly drops.

Further, such metal heaters may have, in the case temperature isincreased, an overshoot phenomenon that the temperature temporarily goesover the set temperature. If the overshoot phenomenon occurs, it takesfurther longer time to bring the temperature of the heating faces of themetal plates to the set temperature.

Additionally, along with the recent tendency of enlargement of thediameter of semiconductor wafers and the like, and other reasons, metalheaters with a larger diameter are desired. With the enlargement of thediameter of the metal plates, the uneven temperature distribution in themetal plates themselves tends to occur, and accordingly, the abovetemperature evenness of the semiconductor wafer is further deteriorated.

In view of the above-mentioned problems, the present inventor has madeextensive research efforts for the purpose of obtaining a metal heaterwhich has a comparatively fast temperature-rising speed and acomparatively short recovery time, hardly causes temperature change in asemiconductor wafer and the like upon heating, and is free from warpingand sagging in metal plates, and found that, by: sandwiching a heatingelement between a plurality of metal plates; and making the thickness ofa metal plate on a heating face side larger than the thickness of ametal plate on the opposite side, it becomes possible to ensure theflatness of the heating face and consequently to maintain thetemperature of the heating face in an even level; thus, a first aspectof the present invention has been completed.

In other words, a metal heater according to a first aspect of thepresent invention comprises a metal plate and a heating element. Herein,the number of the metal plates is a plural number, the heating elementis sandwiched between the metal plates, and the thickness of a metalplate on a heating face side is the same as or larger than the thicknessof a metal plate on a side opposite to said heating face side.

The metal heater according to the first aspect of the present inventioncomprises the plurality of metal plates, and the heater is sandwichedbetween the metal plates. The metal heater having this structure makesit possible to more quickly heat an object to be heated, such as asemiconductor wafer or the like, in comparison with a metal heater thatis formed by a single metal plate with a heater placed on a sideopposite to the heating face side of the metal plate, and also toshorten the recovery time.

Since the metal heater according to the first aspect of the presentinvention is designed so that the thickness of the metal plate on theheating face side is the same as or larger than the thickness of a metalplate on the side opposite to said heating face side, it becomespossible to improve the flatness of the heating face upon heating and,also, to evenly heat the entire semiconductor wafer.

The reason therefor will be briefly described below.

In the metal heater according to the first aspect of the presentinvention, since the thickness of the metal plate on the heating faceside is made larger, the mechanical strength becomes higher, making themetal plate less likely to have warping and the like upon heating.Therefore, upon heating, the flatness of the heating face is improved.

Moreover, in the case where the thickness of the metal plate on theheating face side is made larger, the thermal capacity of the metalplate on the side opposite to said heating face side is made relativelysmaller than the thermal capacity of the metal plate on the heating faceside. For this reason, the metal plate on the side opposite to saidheating face side is made less likely to have accumulation of heat incomparison with the metal plate on the heating face side. Therefore,even in the case where ordinary-temperature silicon wafers aresuccessively placed on the heating face so as to carry out a continuousprocess, heat conduction hardly occurs from the metal plate on the sideopposite to said heating face side to the metal plate on the heatingface side. Of course, temperature change hardly occurs in the metalplate on the heating face side due to an overshoot phenomenon caused bythe heat conduction from the metal plate on the side opposite to saidheating face side to the metal plate on the heating face side.Therefore, it becomes possible to easily control the temperature of themetal plate on the heating face side, and consequently to maintain theheating treatment temperature at a constant level.

The metal heater according to the first aspect of the present inventionmay have a structure in which another metal plate is further attached tothe heating element placed on the metal plate, that is, a structure inwhich a heating element is sandwiched between two metal plates or astructure in which heating elements are sandwiched among three or moremetal plates.

In the case where the metal heater according to the first aspect of thepresent invention comprises three or more metal plates, the thickness ofthe metal plate on the heating face side refers to the thickness ofmetal plates located above the heater of the uppermost layer, and thethickness of the metal plate on the side opposite to said heating faceside refers to the total thickness of the metal plates located below theheater on the uppermost layer.

FIG. 3 shows a structure of a metal heater comprising three metalplates. Herein, FIG. 3 shows only the metal plate and the heater.

In the case of the metal heater as shown in FIG. 3, the thickness of themetal plate on the heating face side refers to a thickness a of a metalplate A located above a heater A of the uppermost layer. Moreover, thethickness of the metal plate on the side opposite to the heating faceside refers to a total thickness b+c of a metal plate B and a metalplate C located below the heater A on the uppermost layer.

In the following, a metal heater having a structure in which a heater issandwiched between two metal plates will be mainly described accordingto the first aspect of the present invention. Here, in the case wherethe metal heater has the structure having two metal plates as describedabove, the metal plate on the heating face side is referred to as anupper metal plate, and the metal plate on the side opposite to saidheating face side is referred to as a lower metal plate.

In the metal heater according to the first aspect of the presentinvention, the lower limit of the thickness of the upper metal plate isdesirably 3 mm.

If the thickness of the upper metal plate is less than 3 mm, thedistance between the heating element and the heating face becomes tooshort; thus, the pattern of the heating element is reflected to thetemperature distribution of the heating face. As a result, it becomesdifficult to evenly heat an object to be heated such as a semiconductorwafer or the like in some cases. In contrast, if the thickness of theupper metal plate is within the above-mentioned range, the pattern ofthe heating element is not reflected to the temperature distribution ofthe heating face so that it becomes possible to evenly heat the objectto be heated.

Moreover, if the thickness of the substrate is within theabove-mentioned range, the metal heater is allowed to have superiormechanical strength without occurrence of warping, sagging and the like,making it possible to positively ensure the flatness of the heatingface.

Furthermore, the lower limit of the thickness of the upper metal plateis more desirably 5 mm.

The upper limit of the thickness of the upper metal plate is desirably50 mm. The thickness of the upper metal plate exceeding 50 mm sometimesmakes it difficult for the temperature of the heating face of the metalplate to follow change in a voltage and an amount of current to beapplied to the heating element, failing to quickly heat the object to beheated, such as a semiconductor wafer or the like, and when thesemiconductor wafer is placed on the heating face, time (recovery time)taken to bring the decreased temperature back to the previoustemperature takes longer to cause a prolonged working time and thesubsequent reduction in productivity.

The upper limit of the thickness of the upper metal plate is moredesirably 30 mm.

Moreover, in the case of the above-mentioned structure, the upper limitof the thickness of the lower metal plate is desirably 50 mm, moredesirably 30 mm, and the lower limit thereof is desirably 1 mm, moredesirably 3 mm.

Furthermore, the ratio of the thickness of the upper metal plate and thethickness of the lower metal plate (thickness of upper metalplate/thickness of lower metal plate) is desirably 1 to 10. When theratio exceeds 10, the thermal capacity of the upper metal plate becomestoo high, sometimes failing to quickly heat the object to be heated.Moreover, when the thermal capacity of the upper metal plate becomes toohigh, the temperature difference between the outermost circumference ofthe heating face and the vicinity of the center portion becomes toolarge, sometimes causing reduction in the temperature evenness on theheating face.

The ratio of the thickness of the upper metal plate and the thickness ofthe lower metal plate is optimally larger than 1 and 10 or less. If theratio of the thickness of the upper metal plate and the thickness of thelower metal plate is within the above-mentioned range, it becomespossible to provide superior temperature evenness on the heating face ina steady state.

In the metal heater according to the first aspect of the presentinvention, the heater is sandwiched between the upper metal plate andthe lower metal plate, and the heating element is formed inside theheater. A circuit constituting the heating element is desirably dividedinto two or more portions.

In the case where the circuit constituting the heating element isdivided into two or more portions, it becomes possible to carry out aprecise temperature controlling operation on the outermost circumferenceof the metal heater, the part of which is more likely to have atemperature drop, and consequently to suppress dispersion in thetemperature of the metal heater.

Moreover, in the metal heater according to the first aspect of thepresent invention, all the diameters of the metal plates and the heaterare desirably the same. This arrangement makes it possible to evenlytransmit heat from the heater to the heating face of the metal plate.

In the case where a heat insulating ring or the like is interposedbetween the metal plate and the supporting case, the diameters of themetal plates may be made different from one another.

In the metal heater according to the first aspect of the presentinvention, the diameter of the metal plates is desirably 200 mm or more.As the diameter of the metal heater becomes larger, the temperature ofthe semiconductor wafer tends to become uneven upon heating; therefore,in such a large diameter, the structure of the first aspect of thepresent invention is allowed to function more effectively. Moreover, asubstrate having such a large diameter makes it possible to receive asemiconductor wafer having a large diameter.

In particular, the diameter of the metal plates is desirably 12 inches(300 mm) or more. This size is mainly used for semiconductor wafers inthe next generation.

In the metal plates constituting the metal heater according to the firstaspect of the present invention, flatness on the surface thereof isdesirably 50 μm or less. In the case where a semiconductor wafer isheated by using the metal heater according to the first aspect of thepresent invention, since the distance between the semiconductor waferand the metal plate is maintained at an almost constant level, theentire semiconductor wafer can be evenly heated. Here, the flatness onthe surface of the metal plate is more desirably 30 μm or less.

In order to realize a metal heater that is superior in flatness, it isnecessary to prevent the metal plate from curving due to pressureimposed from the side faces upon thermal expansion of the metal plate.For this reason, it is desirable to maintain a space between each of theside faces of the metal plate and the supporting case (bottom plate) sothat each of the side faces is not made in contact with the metal plate.

The material of the above-mentioned metal plates desirably has superiorthermal conductivity with high rigidity, and is less likely to bedeformed even when thermally expanded so that, upon completion of themachining processes of the metal plate, the metal plate is desirablyallowed to have a superior flatness.

With respect to the material of the metal plates constituting the metalheater according to the first aspect of the present invention, examplesthereof include aluminum, an aluminum alloy, copper, a copper alloy,stainless, inconel, steel and the like. Among these, an aluminum alloyis desirably used, and an aluminum-copper alloy is more desirably used.Since the aluminum-copper alloy has high mechanical strength, neitherwarping nor distortion takes place due to applied heat even when thethickness of the metal plate is made thinner. For this reason, the metalplate can be made thinner and lighter. Moreover, since thealuminum-copper alloy is also superior in thermal conductivity, thetemperature of the heating face is allowed to follow temperature changein the heating element when it is used as the metal plate. In otherwords, the temperature of the heating element is changed by varying thevoltage and current value so that the heating face temperature of theupper metal plate can be controlled.

In the metal heater according to the first aspect of the presentinvention, the material of the upper metal plate and the material of thelower metal plate are desirably the same. This makes it possible toprevent occurrence of deformations such as warping, sagging and the likein the upper metal plate due to a difference in thermal expansioncoefficients of the materials, and consequently to positively ensure theflatness of the heating face.

Moreover, with respect to the aluminum-copper alloy, other materialssuch as magnesium, manganese, silicon, zinc and the like may be addedthereto in addition to aluminum and copper. This is because, it becomespossible to further improve various functions, such as workability,corrosion resistance and low expansion property.

In the case where aluminum, an aluminum alloy or the like is used as thematerial of the metal plate, the surface of the metal plate is desirablysubjected to an alumite treatment.

This alumite treatment makes it possible to improve the corrosionresistance of the metal plate and, also, to harden the surface thereof;thus, the metal plate is made less likely to have scratches and thelike. Moreover, even when used in actual semiconductorproducing/examining processes, the metal plate is made less likely tohave corrosion due to a resist solution, corrosive gases and the like.

Moreover, a hard alumite treatment can be carried out by performing ananodic oxide coating treatment at a lower temperature, a higher voltage,and a higher current density compared with a common alumite treatment.Such a hard alumite treatment enables to obtain a harder and thinnercoating.

Here, the thickness of the coat film is desirably set to 1 μm or more.In the case of the hard alumite treatment, the thickness of the coatfilm can be set to 3 μm or more.

In the metal heater according to the first aspect of the presentinvention, the outer rim of an area on which the heating element isformed is desirably located at a position within 25% of the diameter ofthe metal plate from the circumference of the metal plate. Since heatradiation takes place from the peripheral edge of the metal plate, thecircumferential portion of the metal plate normally has a temperaturedrop in comparison with the center portion of the metal plate; thus, thetemperature of the heating face tends to become uneven. However, in themetal heater according to the first aspect of the present invention,since the heating element is also disposed at such a peripheral portion,a semiconductor wafer or the like, that is, the object to be heated canbe evenly heated without dispersion in temperature.

Moreover, the heating element is desirably divided into two or moreportions.

If the heating element is divided into two or more portions, therespective heating elements can be temperature-controlled in a separatemanner so that the temperature of the heating face can be maintained ata more even level. More specifically, for example, by preparing theheating element pattern formed on the outermost circumference as acomplex divided pattern, a precise temperature controlling operation canbe carried out on the outermost circumference of the metal heater thattends to have a temperature drop; thus, it becomes possible to suppressdispersion in the temperature of the heating face.

In the metal heater according to the first aspect of the presentinvention, a wafer guide ring may be placed at a side face of the metalplate, or it may be placed at the peripheral edge or the surface of theheating face of the metal plate.

In the case where the metal heater is attached to a supporting case andused, a gas flow is generated from the metal plate side toward asemiconductor wafer placed on the metal heater; thus, this gas flowtends to make it difficult to maintain the evenness in temperature ofthe semiconductor wafer. However, the provision of the wafer guide ringcan prevent the gas flow toward the semiconductor wafer; therefore, itbecomes possible to further ensure the evenness in temperature of thesemiconductor wafer.

In view of the above-mentioned problems, the present inventor has madeextensive research efforts for the purpose of obtaining a metal heaterwhich has a comparatively fast temperature-rising speed and acomparatively short recovery time, and can evenly heat an object to beheated such as a semiconductor wafer or the like, without causingwarping and sagging in its metal plate, and found that, by: sandwichinga heating element between a plurality of metal plates; and forming thesemetal plates from the same material, it becomes possible to ensure theflatness of the heating face and consequently to maintain thetemperature of the heating face at an even level; thus, a second aspectof the present invention has been completed.

That is, a metal heater according to a second aspect of the presentinvention comprises a plurality of metal plates and a heating element,with the heating element sandwiched between the metal plates. Herein,the plurality of metal plates are made of the same material.

The metal heater according to the second aspect of the present inventioncomprises the plurality of metal plates, and the heater is sandwichedbetween the metal plates. In comparison with a metal heater that isformed by a single metal plate with a heater provided on the face on theside opposite to the heating face side of the metal plate, since themetal heater having this structure makes the thickness of the metalplate located on the heating face side of the heater thinner than theabove-mentioned single metal plate, it becomes possible to more quicklyheat an object to be heated, such as a semiconductor wafer or the like,and also to shorten the recovery time.

In the metal heater according to the second aspect of the presentinvention, since the plurality of metal plates are made of the samematerial, even when the temperature of the metal heater is raised orlowered, the plurality of the metal plates are expanded or shrunk at thesame ratio. Therefore, even when these metal plates are secured withsecuring screws, neither warping nor sagging occurs in the metal plateon the heating face side of the heater so that it becomes possible tomaintain the flatness of the heating face upon heating and, also, tomake the distance between the semiconductor wafer and the heating faceconstant; thus, the entire semiconductor wafer can be heated evenly.

In the metal heater according to the second aspect of the presentinvention, with respect to the plurality of metal plates, the thicknessof the metal plate (upper metal plate) on the heating face side of theheater is desirably made larger than the thickness of the metal plate(lower metal plates) on the opposite side.

Moreover, in the case where the thickness of the metal plate on theheating face side is made larger, the thermal capacity of the metalplate on the side opposite to the heating face side is made relativelysmaller than the thermal capacity of the metal plates on the heatingface side. For this reason, the metal plate on the side opposite to theheating face side is made less likely to have accumulation of heat incomparison with the metal plate on the heating face side. Therefore,even in the case where ordinary-temperature silicon wafers aresuccessively placed on the heating face so as to carry out a continuousprocess, heat conduction hardly occurs from the metal plate on the sideopposite to the heating face side to the metal plate on the heating faceside. Of course, temperature change hardly occurs in the metal plate onthe heating face side due to an overshoot phenomenon caused by the heatconduction from the metal plate on the side opposite to the heating faceside to the metal plate on the heating face side. Therefore, it becomespossible to easily control the temperature of the metal plate on theheating face side, and consequently to maintain the heating treatmenttemperature at a constant level.

The metal heater according to the second aspect of the present inventionmay have a structure in which another metal plate is further attached tothe heating element placed on the metal plate, that is, a structure inwhich a heating element is sandwiched between two metal plates, or astructure in which heating elements are sandwiched among three or moremetal plates. In the case where the metal heater according to the secondaspect of the present invention has three or more metal plates, thethickness of the metal plate on the heating face side (upper metalplate) and the thickness of the metal plate on the side opposite to theheating face side (lower metal plate) are defined in the same manner asthose of the first aspect of the present invention.

In the following, a metal heater having a structure in which a heater issandwiched between two metal plates will be mainly described accordingto the second aspect of the present invention.

In metal heater according to the second aspect of the present invention,the lower limit of the thickness of the upper metal plate is desirably 3mm. The reason therefor is the same as that described in the firstaspect of the present invention. Moreover, the lower limit of thethickness of the upper metal plate is more desirably 5 mm.

The upper limit of the thickness of the upper metal plate is desirably50 mm. The reason therefor is the same as that described in the firstaspect of the present invention. The upper limit of the thickness of theupper metal plate is more desirably 30 mm.

Moreover, in the case of the above-mentioned structure, the upper limitof the thickness of the lower metal plate is desirably 50 mm, moredesirably 30 mm, and the lower limit thereof is desirably 1 mm, moredesirably 3 mm.

Furthermore, the ratio of the thickness of the upper metal plate and thethickness of the lower metal plate (thickness of upper metalplate/thickness of lower metal plate) is desirably 1 to 10. The reasontherefor is the same as that described in the first aspect of thepresent invention. In particular, the ratio is optimal in a caseexceeding 1. Thus, it becomes possible to provide superior temperatureevenness on the heating face in a steady state.

In the metal heater according to the second aspect of the presentinvention, the heater is sandwiched between the upper metal plate andthe lower metal plate, with the heating element formed inside theheater. In the same manner as the first aspect of the present invention,a circuit constituting the heating element is desirably divided into twoor more portions, and all the diameters of the plurality of metal platesand the heater are desirably the same. In the case where a heatinsulating ring or the like is interposed between the metal plate andthe supporting case, the diameters of the metal plates may be madedifferent from one another.

In the metal heater according to the second aspect of the presentinvention, the diameter of the metal plates is desirably 200 mm or more,more desirably 12 inches (300 mm) or more. The reason therefor is thesame as that described in the first aspect of the present invention.

In the metal plates constituting the metal heater according to thesecond aspect of the present invention, the flatness on the surfacethereof is desirably 50 μm or less, more desirably 30 μm or less. Thereason therefor is the same as that described in the first aspect of thepresent invention.

In order to realize a metal heater that is superior in flatness, it isnecessary to prevent the metal plate from curving due to pressureimposed from the side faces upon thermal expansion of the metal plate.For this reason, it is desirable to maintain a space between each of theside faces of the metal plate and the supporting case (bottom plate) sothat each of the side faces is not made in contact with the metal plate.

In the second aspect of the present invention, the plurality of metalplates are made of the same material, and the material of the metalplates desirably has a superior thermal conductivity with high rigidity,and is less likely to be deformed even when thermally expanded so that,upon completion of the machining processes of the metal platesthemselves, each metal plate is desirably allowed to have a superiorflatness. With respect to the material of the metal plates, for example,the same materials and the like as in the first aspect of the presentinvention may be used.

With respect to the material of the metal plates constituting the metalheater according to the second aspect of the present invention, analuminum alloy is desirably used, and an aluminum-copper alloy is moredesirably used, for the same reason as that described in the firstaspect of the present invention. In the same manner as the first aspectof the present invention, with respect to the aluminum-copper alloy,other materials such as magnesium, manganese, silicon, zinc and the likemay be added thereto in addition to aluminum and copper.

In the case where aluminum, an aluminum alloy or the like is used as thematerial of the metal plate, the surface of the metal plate is desirablysubjected to an alumite treatment as in the same manner described in thefirst aspect of the present invention.

Here, after the alumite treatment, the thickness of the coat film isdesirably 1 μm or more, and in the case of the hard alumite treatment,the thickness of the coat film may be set to 3 μm or more.

In the metal heater according to the second aspect of the presentinvention, the peripheral edge of an area on which the heating elementis formed is desirably located at a position within 25% of the diameterof the metal plate from the periphery of the metal plate.

Moreover, the heating element is desirably divided into two or moreportions. In the metal heater according to the second aspect of thepresent invention, a wafer guide ring may be placed at a side face ofthe metal plate, or it may be placed at the peripheral edge or thesurface of the heating face of the metal plate. The reason therefor isthe same as that described in the first aspect of the present invention.

In the metal heater according to the second aspect of the presentinvention, a convex portion for supporting an object to be heated isdesirably placed on the heating face opposing the object to be heated ofthe metal plate corresponding to an area on which a heating element isformed. Thus, it becomes possible to make a semiconductor wafer or thelike, that is, the object to be heated, less likely to have sagging and,also, to make the distance between the semiconductor wafer or the likeand the heating face of the metal plate constant so that the entiresemiconductor wafer or the like can be heated evenly.

In the second aspect of the present invention, the terms “a convexportion for supporting an object to be heated is placed corresponding toan area on which a heating element is formed” and “an area on which aheating element is formed” are used under the same definitions as thoseof a third aspect of the present invention, which will be describedlater.

With respect to the number of the above-mentioned convex portions, ifthe diameter of the area on which a heating element is formed is 250 mmor more and less than 300 mm, the number is desirably 6 or more. If thediameter of the area on which a heating element is formed is 200 mm ormore and less than 250 mm, the number is desirably 5 or more. If thediameter of the area on which a heating element is formed is 300 mm ormore, the number is desirably 7 or more. The reason therefor is the sameas that which will be described in the third aspect of the presentinvention.

With respect to the upper limit of the number of the convex portionsformed on the heating face of the metal plate, although not particularlylimited, if the diameter of the area on which a heating element isformed is 250 mm or more and less than 300 mm, the number is desirably20 or less. If the diameter of the area on which a heating element isformed is 200 mm or more and less than 250 mm, the number is desirably15 or less. The reason therefor is the same as that which will bedescribed in the third aspect of the present invention.

Moreover, with respect to positions at which the convex portions areformed, for example, the same layout as that which will be described inthe third aspect of the present invention later may be used.

The positions at which the convex portions are formed are desirablywidely dispersed on the metal plate, with the positions beingrotation-symmetrical with respect to the center. The reason therefor isthe same as that which will be described in the third aspect of thepresent invention.

In the case where the convex portions are placed on the metal plate in abiased manner and/or the convex portions are placed with irregularintervals, a portion having a wide interval between the convex portionsis formed, and in such a portion, the semiconductor wafer tends to havesagging; as a result, the distance between the semiconductor wafer andthe metal plate tends to become uneven, making it difficult to evenlyheat the semiconductor wafer.

With respect to a method for placing the convex portions on the heatingface of the metal plate, the same method as that used for the followingthird aspect of the present invention may be used.

With respect to a method for securing supporting pins into the concaveportions, the same method as that used for the following third aspect ofthe present invention may be used.

With respect to the metal heater according to the second aspect of thepresent invention, those metal heaters in which the diameter of the areaon which the heating element is formed is 250 mm or more, with six ormore supporting pins placed on the heating face of the metal plate maybe optimally used. Moreover, at least one supporting pin is desirablyplaced in the center of the area in which the heating element is formed.

With respect to the shape of the supporting pin, for example, a pinnacleshape with a cone on the tip, a pinnacle shape with a pyramid on thetip, a semi-spherical shape or the like may be desirably used. Here, inthe case where the shape of the supporting pin other than the tip is acylindrical shape, the diameter thereof is desirably 1 to 10 mm.Moreover, the height of the cylindrical-shaped portion of the supportingpin is desirably 1 to 10 mm. The reason therefor is the same as thatwhich will be described in the third aspect of the present invention.

In the case where the supporting pin has a head portion shaped like anail, the head portion is desirably formed into a shape and a size thatare suitably fitted to each concave portion. The reason therefor is thesame as that which will be described in the third aspect of the presentinvention.

The supporting pins are desirably made of ceramics, and in considerationof abrasion resistance to silicon wafers with comparatively littlethermal deformation, productivity, costs and the like, oxide ceramicmaterials such as alumina, silica and the like are desirably used.

In the above-mentioned metal heater, the supporting pins are desirablydesigned so as to protrude from the heating face of the metal plate withthe same height. The reason therefor is the same as that which will bedescribed in the third aspect of the present invention.

The height at which the supporting pin protrudes from the metal plate isdesirably 5 to 5000 μm, that is, in a state where the object to beheated is held so as to be apart from the heating face of the metalplate by 5 to 5000 μm. The reason therefor is the same as that whichwill be described in the third aspect of the present invention.

The distance between the object to be heated and the heating face of themetal plate is desirably 5 to 500 μm, more desirably 20 to 200 μm.

The diameters of the concave portion in which the supporting pin isplaced and the through hole used for the supporting pin are desirably 1to 10 mm. Moreover, the depth of each concave portion is desirably 1 to10 mm. The reason therefor is the same as that which will be describedin the third aspect of the present invention.

In view of the above-mentioned problems, the present inventor has madeextensive research efforts for the purpose of obtaining a metal heaterwhich is superior in temperature evenness in surface in transitionperiod, has a comparatively short recovery time, and can evenly heat anobject to be heated such as a semiconductor wafer, without causingsagging in the object to be heated upon heating, and found that by:sandwiching a heating element between a plurality of metal plates; andproviding convex portions on a heating face opposing the object to beheated of the metal plate corresponding to an area on which the heatingelement is formed, it becomes possible to evenly heat the object to beheated, without causing any sagging in the semiconductor wafer; thus,the third aspect of the present invention has been completed.

That is, a metal heater according to the third aspect of the presentinvention comprises a plurality of metal plates and a heating element,with the heating element sandwiched between the metal plates. Herein, aconvex portion for supporting an object to be heated is placed on aheating face opposing the object to be heated of the metal platecorresponding to an area on which the heating element is formed.

The metal heater according to the third aspect of the present inventioncomprises the plurality of metal plates, and the heater is sandwichedbetween the metal plates. In comparison with a metal heater that isformed by a single metal plate with a heater provided on the face on theside opposite to the heating face side of the metal plate, since themetal heater having this structure makes the thickness of the metalplate located on the heating face side of the heater thinner than theabove-mentioned single metal plate, it becomes possible to more quicklyheat an object to be heated, such as a semiconductor wafer or the like,and also to shorten the recovery time.

In the metal heater according to the third aspect of the presentinvention, since convex portions for supporting an object to be heatedare placed on the heating face opposing the object to be heated of themetal plate corresponding to the area in which the heating element isformed, it becomes possible to make the semiconductor wafer or the like,that is, the object to be heated, less likely to have sagging.Consequently, it is possible to make the distance between thesemiconductor wafer or the like and the heating face of the metal plateconstant; thus, the entire semiconductor wafer can be heated evenly.

In the third aspect of the present invention, the term, “a convexportion for supporting an object to be heated is placed corresponding toan area on which a heating element is formed”, refers to a structure inwhich an appropriate number of convex portions are placed at appropriatepositions on the heating face of the metal plate corresponding to thesize of the area on which the heating element of the metal plate isformed and the size of the semiconductor wafer to be heated.

Here, the term, “an area on which a heating element is formed”, isdefined as follows: when the heating element pattern formed on the metalplate is perpendicularly shifted onto the heating face of the metalplate, the area corresponds to an inner area of the minimum circle thatincludes all of the heating element pattern.

With respect to the number of the convex portions, if the diameter ofthe area on which a heating element is formed is 250 mm or more and lessthan 300 mm, the number is desirably 6 or more. If the number of theconvex portions is less than 6, the interval between the convex portionsbecomes too wide; as a result, the semiconductor wafer tends to havesagging to cause dispersion in the distance between the semiconductorwafer and the metal plate, and the subsequent difficulty in evenlyheating the entire semiconductor wafer. If the diameter of the area onwhich a heating element is formed is 200 mm or more and less than 250mm, the number of the convex portions is desirably 5 or more. If thediameter of the area on which a heating element is formed is 300 mm ormore, the number thereof is desirably 7 or more.

With respect to the upper limit of the number of the convex portionsformed on the heating face of the metal plate, although not particularlylimited, if the diameter of the area on which a heating element isformed is 250 mm or more and less than 300 mm, the number is desirably20 or less. This arrangement is prepared from the viewpoints of avoidingcomplex manufacturing processes, of cutting manufacturing costs, and ofmaintaining the temperature of the heating face in a more even level. Inthe case where the diameter of the area on which a heating element is200 mm or more and less than 250 mm, the number of the convex portionsis desirably set to 15 or less.

Moreover, with respect to positions at which the convex portions areformed, for example, a layout in which on an area forming acomparatively circumferential portion of the metal plate, a plurality ofconvex portions are placed on circumferences of concentric circles ofthe metal plate with equal intervals, with a single supporting pinattached to the center of the metal plate, may be used, or anotherlayout in which on an area forming a comparatively circumferentialportion of the metal plate, a plurality of supporting pins arerespectively placed on circumferences of concentric circles of theprotruding metal plate as well as on circumferences of concentriccircles corresponding to the inner circumference thereof, with a singlesupporting pin attached to the center of the metal plate, may be used.

The positions at which the convex portions are formed are desirablywidely dispersed on the metal plate, with the positions beingrotation-symmetrical with respect to the center. The reason therefor isas follows. By providing the convex portions at the above-mentionedpositions, upon heating a semiconductor wafer, the semiconductor waferis made free from sagging, and the distance between the semiconductorwafer and the metal plate is made almost constant so that the heatingprocess is carried out on the semiconductor wafer evenly.

In the case where the convex portions are placed on the metal plate in abiased manner and/or the convex portions are placed with irregularintervals, a portion having a wide interval between the convex portionsis formed, and in such a portion, the semiconductor wafer tends to havesagging; as a result, the distance between the semiconductor wafer andthe metal plate tends to become uneven, making it difficult to evenlyheat the semiconductor wafer.

For example, each of the convex portions may be placed on the heatingface of the metal plate by forming a concave portion on the heating faceof the metal place and inserting a supporting pin in the concave portionso as to secure the convex portion therein, or may be attached onto theheating face by forming a through hole in the metal plate and insertinga supporting pin in the through hole so as to secure the convex portiontherein. Here, the through hole for the supporting pin and the concaveportion may be formed in combination.

By using these methods, the supporting pin can be secured onto the metalplate comparatively easily.

With respect to a method for fixedly securing the supporting pin in theconcave portion, for example, a method in which a supporting pin havinga head portion like a nail is inserted to a concave portion formed as acylindrical-shaped hollow portion formed in the heating face of themetal plate with the head portion placed on the metal plate side, and aspring having a C-shape is fitted to the concave portion in a manner soas to surround the supporting pin so that the supporting pin is fixedlysecured thereon by using the spring force, may be used.

By using such a method, the supporting pin is positively secured thereonwithout coming off from the metal plate.

With respect to the metal heater according to the third aspect of thepresent invention, those metal heaters in which the diameter of the areaon which the heating element is formed is set to 250 mm or more, withsix or more supporting pins being attached to the heating face of themetal plate may be optimally used. Moreover, at least one supporting pinis desirably placed in the center of the area on which the heatingelement is formed.

With respect to the shape of the supporting pin, for example, a pinnacleshape with a cone on the tip, a pinnacle shape with a pyramid on thetip, a semi-spherical shape or the like may be desirably used. When asemiconductor wafer is placed on the supporting pins having such ashape, the semiconductor wafer is supported through point contacts,making the semiconductor wafer free from formation of hot spots and thelike.

Here, in the case where the shape of the supporting pin other than thetip is a cylindrical shape, the diameter thereof is desirably 1 to 10mm. Upon placing the semiconductor wafer, the diameter of less than 1 mmtends to fail to provide a stable supporting function as the supportingpin, while the diameter exceeding 10 mm tends to cause hot spots and thelike on the semiconductor wafer.

Moreover, the height of the cylindrical-shaped portion of the supportingpin is desirably 1 to 10 mm. The height of less than 1 mm tends to failto positively secure the supporting pin onto the heating face of themetal plate, while the height exceeding 10 mm tends to fail to evenlyheat the semiconductor wafer.

In the case where the supporting pin has a head portion shaped like anail, the head portion is desirably formed into a shape and a size thatare suitably fitted to each concave portion. When the head portion istoo small in comparison with the size of the concave portion, thesupporting pin becomes unstable.

The supporting pins are desirably made of ceramics, and in considerationof abrasion resistance to silicon wafers with comparatively littlethermal deformation, productivity and costs, oxide ceramic materialssuch as alumina, silica and the like are desirably used.

In the above-mentioned metal heater, the supporting pins are desirablydesigned so as to protrude from the heating face of the metal plate withthe same height. In the case where all the heights by which thesupporting pins protrude are made the same, upon placing a semiconductorwafer, the semiconductor wafer is made in parallel with the heating faceof the metal plate, and since all the supporting pins are allowed tosupport the semiconductor wafer, no sagging occurs. Consequently, thedistance between the semiconductor wafer and the metal plate ismaintained in an even level so that the semiconductor wafer can beevenly heated. In contrast, when the heights by which the supportingpins protrude are different from one another, the semiconductor wafertends to tilt, or those supporting pins having short heights are notmade in contact with the semiconductor wafer to cause sagging.Consequently, dispersion tend to occur in the distance between thesemiconductor wafer and the metal plate, making it difficult to evenlyheat the semiconductor wafer.

The height at which the supporting pin protrudes from the heating faceof the metal plate is desirably 5 to 5000 μm, that is, in a state inwhich the object to be heated is apart from the heating face of themetal plate by 5 to 5000 μm. The height of less than 5 μm tends to makethe temperature of the semiconductor wafer uneven due to influences fromthe temperature distribution of the metal plate, and might cause thewafer to come into contact with the metal plate. The height exceeding5000 μm makes it difficult to raise the temperature of the semiconductorwafer to cause a temperature drop, in particular, on the peripheralportion of the semiconductor wafer.

The distance between the object to be heated and the heating face of themetal plate is desirably 5 to 500 μm, more desirably 20 to 200 μm.

The diameters of the concave portion in which the supporting pin isplaced and the through hole for the supporting pin are desirably 1 to 10mm. The diameter of less than 1 mm tends to fail to positively securethe supporting pin, while the diameter exceeding 10 mm tends to causecooling spots.

Moreover, the depth of each concave portion is desirably 1 to 10 mm. Thedepth of less than 1 mm might cause the supporting pins to come off,while the depth exceeding 10 mm tends to cause cooling spots.

In the metal heater according to the third aspect of the presentinvention, with respect to the plurality of metal plates, the thicknessof the metal plate (upper metal plate) on the heating face side of theheater is desirably made larger than the thickness of the metal plate(lower metal plates) on the opposite side. The reason therefor is thesame as that in the metal heater according to the second aspect of thepresent invention.

The metal heater according to the third aspect of the present inventionmay have a structure in which another metal plate is further attached tothe heating element placed on the metal plate, that is, a structure inwhich a heating element is sandwiched between two metal plates, or astructure in which heating elements are sandwiched among three or moremetal plates. In the case where the metal heater according to the thirdaspect of the present invention has three or more metal plates, thethickness of the metal plate on the heating face side (upper metalplate) and the thickness of the metal plate on the side opposite to theheating face side (lower metal plate) are defined in the same manner asthose of the first aspect of the present invention.

In the following, a metal heater in which a heater is sandwiched betweentwo metal plates will be mainly described according to the third aspectof the present invention.

In metal heater according to the third aspect of the present invention,the lower limit of the thickness of the upper metal plate is desirably 1mm. In the case where the thickness of the upper metal plate is lessthan 1 mm, the distance between the heating element and the heating facebecomes too short; thus, the pattern of the heating element is reflectedto the temperature distribution of the heating face. As a result, itbecomes difficult to evenly heat an object to be heated such as asemiconductor wafer or the like in some cases. In contrast, when thethickness of the upper metal plate is within the above-mentioned range,the pattern of the heating element is not reflected to the temperaturedistribution of the heating face so that it becomes possible to evenlyheat the object to be heated.

Moreover, when the thickness of the substrate is within theabove-mentioned range, the metal heater is allowed to have superiormechanical strength without occurrence of warping, sagging and the likein the metal plate, making it possible to positively ensure the flatnessof the heating face.

Furthermore, the lower limit of the thickness of the upper metal plateis more desirably 5 mm.

The upper limit of the thickness of the upper metal plate is desirably50 mm. The thickness of the upper metal plate exceeding 50 mm sometimesmakes it difficult for the temperature of the heating face of the metalplate to follow a voltage to be applied to the heating element andchange in the amount of electric current, failing to quickly heat anobject to be heated, such as a semiconductor wafer or the like, and whenthe semiconductor wafer is placed on the heating face, time (recoverytime) taken to bring the decreased temperature back to the previoustemperature takes longer to cause a prolonged working time and thesubsequent reduction in productivity.

In the above-mentioned structure, the upper limit of the thickness ofthe lower metal plate is desirably set to 50 mm, more desirably 30 mm,and the lower limit thereof is desirably 1 mm, more desirably 3 mm.

Moreover, the ratio of the thickness of the upper metal plate and thethickness of the lower metal plate (thickness of upper metalplate/thickness of lower metal plate) is desirably 1 to 10. The reasontherefor is the same as that described in the first aspect of thepresent invention. In particular, the ratio exceeding 1 is optimallyused. Thus, it becomes possible to provide superior temperature evennesson the heating face in steady state.

In the metal heater according to the third aspect of the presentinvention, the heater is sandwiched between the upper metal plate andthe lower metal plate, and the heating element is formed inside theheater. In the same manner as the first aspect of the present invention,a circuit constituting the heating element is desirably divided into twoor more portions, and all the diameters of the plurality of metal platesand the heater are desirably the same. In the case where a heatinsulating ring or the like is interposed between the metal plate andthe supporting case, the diameters of the metal plates may be madedifferent from one another.

In the metal heater according to the third aspect of the presentinvention, the diameter of the metal plates is desirably 200 mm or more,more desirably 12 inches (300 mm) or more. The reason therefor is thesame as that described in the first aspect of the present invention.

In the metal plates constituting the metal heater according to the thirdaspect of the present invention, the flatness on the surface thereof isdesirably 50 μm or less, more desirably 30 μm or less. The reasontherefor is the same as that described in the first aspect of thepresent invention.

In order to realize a metal heater that is superior in its flatness, itis necessary to prevent the metal plate from curving due to pressureimposed from the side faces upon thermal expansion of the metal plate.For this reason, it is desirable to maintain a space between each of theside faces of the metal plate and the supporting case (bottom plate) sothat the side faces is not made in contact with the metal plate.

In the third aspect of the present invention, the plurality of metalplates are desirably made of the same material. Moreover, the materialof the metal plates desirably has a superior thermal conductivity withhigh rigidity, and is less likely to be deformed even when thermallyexpanded so that, upon completion of the machining processes of themetal plates themselves, the metal plates are desirably allowed to havea superior flatness. With respect to the material of the metal plates,for example, the same material as that used in the first aspect of thepresent invention, and the like are proposed.

Also in the third aspect of the present invention, an aluminum alloy isdesirably used, and an aluminum-copper alloy is more desirably used inthe same manner as the first aspect of the present invention. Moreover,with respect to the aluminum-copper alloy, other materials such asmagnesium, manganese, silicon, zinc and the like may be added thereto.

In the case where aluminum, an aluminum alloy or the like is used as thematerial of the metal plate, the surface of the metal plate is desirablysubjected to an alumite treatment in the same manner as the first aspectof the present invention.

In the case of the alumite treatment, the thickness of the coat film isdesirably 1 μm or more, and in the case of a hard alumite treatment, thethickness of the coat film may be set to 3 μm or more.

In the metal heater according to the third aspect of the presentinvention, the peripheral edge of an area in which the heating elementis formed is desirably located at a position within 25% of the diameterof the metal plate from the periphery of the metal plate.

Moreover, the heating element is desirably divided into two or moreportions. In the metal heater according to the third aspect of thepresent invention, a wafer guide ring may be placed at a side face ofthe metal plate, or it may be placed at the peripheral edge or thesurface of the heating face of the metal plate. The reason therefor isthe same as that described in the first aspect of the present invention.

The metal heater according to the third aspect of the present inventionmay be used as a heater module or the like by fixedly securing anoptical waveguide such as quartz or the like thereon. In this case, theoptical waveguide may be supported by convex portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view that schematically shows one example ofa metal heater according to a first aspect of the present invention.

FIG. 2 is a horizontal cross-sectional view of a heater that constitutesa part of the metal heater shown in FIG. 1.

FIG. 3 is a cross-sectional view that schematically shows a metal plateand the heater of the metal heater according to the first aspect of thepresent invention.

FIG. 4(a) is a cross-sectional view that schematically shows anotherexample of a conventional metal heater, and FIG. 4(b) is a plan view ofFIG. 4(a).

FIG. 5(a) is a cross-sectional view that schematically shows one exampleof a metal heater according to a second aspect of the present invention.FIG. 5(b) schematically shows a method by which a heating element and aconductive line are joined to each other by caulking using a joiningfoil in the metal heater shown in FIG. 5(a).

FIG. 6(a) is a cross-sectional view that schematically shows one exampleof a metal heater according to a third aspect of the present invention.FIG. 6(b) schematically shows a method by which a heating element and aconductive line are joined to each other by caulking using a joiningfoil in the metal heater shown in FIG. 6(a).

FIG. 7 is a plan view that shows the metal heater shown in FIG. 6(a).

FIG. 8 shows a three dimensional shape of a part of a metal heaterheating face according to Example 1 at ordinary temperature.

FIG. 9 shows a three dimensional shape of a part of a metal heaterheating face in according with Example 1 at 140° C.

FIG. 10 shows a three dimensional shape of a part of a metal heaterheating face according to Test Example 1 at 140° C.

FIG. 11 shows a three dimensional shape of a part of a metal heaterheating face according to Example 8 at ordinary temperature.

FIG. 12 shows a three dimensional shape of a part of a metal heaterheating face in according with Example 8 at 140° C.

FIG. 13 shows a three dimensional shape of a part of a metal heaterheating face according to Test Example 3 at 140° C.

FIG. 14 is a graph that shows a relationship between a wafer temperatureand time in the vicinity of 100° C. when a metal heater according toExample 12 is used.

FIG. 15 is a graph that shows a relationship between a wafer temperatureand time in the vicinity of 120 to 130° C. when the metal heateraccording to Example 12 is used.

FIG. 16 is a graph that shows a relationship between a wafer temperatureand time in the vicinity of 140° C. when the metal heater according toExample 12 is used.

FIG. 17 is a graph that shows a relationship between a wafer temperatureand time in the vicinity of 100° C. when the metal heater according toExample 16 is used.

FIG. 18 is a graph that shows a relationship between a wafer temperatureand time in the vicinity of 120 to 130° C. when the metal heateraccording to Example 16 is used.

FIG. 19 is a graph that shows a relationship between a wafer temperatureand time in the vicinity of 140° C. when the metal heater according toExample 16 is used.

FIG. 20 shows a three dimensional shape of a part of a metal heaterheating face according to Example 12 at ordinary temperature.

FIG. 21 shows a three dimensional shape of a part of a metal heaterheating face in according with Example 12 at 140° C.

FIG. 22 shows a three dimensional shape of a part of a metal heaterheating face according to Comparative Example 2 at 140° C.

EXPLANATION OF SYMBOLS

-   410, 510, 610 Metal heater-   411, 511, 611 Upper metal plate-   411 a, 511 a, 611 a Heating face-   412, 512, 612 Heater-   414, 514, 614 Bottomed hole-   415, 515, 615 Through hole-   416, 516, 616 Temperature measuring element-   417, 517, 617 Metal plate securing screw-   418, 518, 618 Supporting pin-   419, 519, 619 Semiconductor wafer-   420, 520, 620 Supporting case-   421, 521, 621 Lower metal plate-   422, 522, 622 Pressing plate-   423, 523, 623 Heat shielding plate-   424, 524, 624 Conductive line-   425 Heating element-   525, 625 Supporting plate-   426 Mica plate-   627 Spring-   628 Concave portion-   529, 629 Stainless foil-   530, 630 Stainless foil for connection-   531, 631 Attaching member-   532, 632 Barrier ring

DETAILED DISCLOSURE OF THE INVENTION

In the following, description will be given of metal heaters accordingto the first to third aspects of the present invention in succession.

First, an embodiment of the first aspect of the present invention willbe described.

The metal heater according to the first aspect of the present inventionis a metal heater comprising a metal plate and a heating element.Herein, the number of the metal plates is a plural number, the heatingelement is sandwiched between the metal plates, and the thickness of ametal plate on a heating face side is the same as or larger than thethickness of a metal plate on a side opposite to the heating face side.

Referring to the drawings, description will be given of a metal heaterin which a heater is sandwiched between two metal plates as one exampleof the metal heater according to the first aspect of the presentinvention.

FIG. 1 is a cross-sectional view that schematically shows the metalheater of this type, and FIG. 2 is a horizontal cross-sectional view ofa heater that constitutes a part of the metal heater shown in FIG. 1.

In this metal heater 410, a heater 412 is sandwiched between an uppermetal plate 411 and a lower metal plate 421, each of which has a diskshape, and the upper metal plate 411, the heater 412 and the lower metalplate 421 are fixedly secured to, and tightly bound to one anotherthrough metal plate securing screws 417 so that heat from the heater 412is suitably transmitted to the upper metal plate 411.

Moreover, the thickness of the upper metal plate 411 is made larger thanthe thickness of the lower metal plate 421. Therefore, as has beendescribed already, the flatness of the heating face is maintained, andthe temperature of the heating face is equalized so that the object tobe heated can be evenly heated.

By securing the metal plate using the metal plate securing screws 417,the thickness of the metal plate becomes substantially large so that theflatness of the heating face is further improved.

The metal heater 410 according to the first aspect of the presentinvention makes it possible to realize a flatness of 50 μm or less on aheating face 411 a of the upper metal plate 411. By realizing such aflatness, upon heating a semiconductor wafer, the distance between thesemiconductor wafer and the metal plate is made almost constant so thatthe heating process is carried out on the entire semiconductor waferevenly.

In the metal heater 410 according to the first aspect of the presentinvention, the side faces of the upper metal plate 411, the heater 412and the lower metal plate 421 are not made in tightly contact with asupporting case 420, and secured in a non-contact state. With thisstructure, the metal plate can be prevented from being curved due topressure from the side faces when the upper metal plate 411 has beenthermally expanded, and upon heating an object to be heated, heatreleased from the metal plate and the like is reduced so that an objectto be heated can be heated more quickly in comparison with the case inwhich the side faces of the upper metal plate 411, the heater 412 andthe lower metal plate 421 are made in tightly contact with thesupporting case 420. In this case, an air layer is allowed to functionas a heat insulating material.

Moreover, the metal heater 410 has a structure in which the metal platesecuring screws 417 do not penetrate supporting case 420, and are onlyallowed to penetrate the upper metal plate 411, the heater 412 and thelower metal plate 421, and designed to secure these members. With thisstructure, it becomes possible to prevent deformation in the upper metalplate 411 due to a difference in thermal expansion coefficients betweenthe upper metal plate 411 and the supporting case 420, and also toreduce heat released from the upper metal plate 411 and the like uponheating an object to be heated so that the object to be heated can beheated quickly.

A heat shielding plate 423 is placed on the bottom portion of thesupporting case 420 so that it becomes possible to prevent heat,released from the upper metal plate 411 and the lower metal plate 421,from conducting to the device. Here, a barrier ring 428 is placed on theperipheral edge of the supporting case 420. The provision of the barrierring 428 makes it possible to prevent outside gases from flowing thereinto cause a temperature change in the heating face 411 a.

Moreover, a bottomed hole 414 is formed in the metal heater 410, and atemperature measuring element 416 configured to measure the temperatureof the upper metal plate 411 is inserted into the bottomed hole 414, andsealed with an inorganic adhesive or the like (not shown) to be securedtherein.

In the metal heater 410, supporting pins 418, each having apinnacle-like tip, are placed on the heating face, and the semiconductorwafer 419 is supported through the supporting pins 418 so that thesemiconductor wafer 419 can be heated with a fixed distance kept fromthe heating face of the upper metal plate 411.

In the metal heater according to the first aspect of the presentinvention, with respect to the number of the supporting pins, althoughnot particularly limited, it is desirably set to six or more in the casewhere, for example, the diameter of the metal plate is 12 inches (300mm) or more. When the number of the supporting pins is six or more, aclearance between the heating face and the semiconductor wafer isaccurately maintained so that it becomes possible to easily maintain theevenness of temperature on the heating face in transition period.

Moreover, the metal heater 410 is also provided with through holes 415each of which penetrates the upper metal plate 411, the heater 412, thelower metal plate 421 and the supporting case 420, and by insertingpillar-shaped lifter pins and the like through the through holes 415, asemiconductor wafer 419, that is, the object to be heated is supportedwith a fixed distance kept from the heating face 411 a of the uppermetal plate 411 so that the semiconductor wafer 419 can be properlytransported.

Here, the heater 412 is connected to a conductive line 424, and theconductive line 424 is led outside from a through hole formed in thesupporting case 420 and the heat shielding plate 423, and connected to apower supply or the like (not shown).

In the metal heater 410 shown in FIG. 1, a part of the heating element425 made of a metal foil such as stainless foil or the like is exposeddown to the lower side of the through hole formed in the lower metalplate 421 so that one end of the conductive line 424 is wrapped with theexposed foil (hereinafter, referred to as foil for connection), and anattaching member 427 made of metal having a caulking portion (not shown)is then attached thereto; thus, the caulking portion of the attachingmember 427 is caulked so that the heating element 425 and the conductiveline 424 are connected to each other.

Alternatively, the conductive line 424 may be connected to a heatingelement placed inside the heater 412 on the side face of the heater 412.

Moreover, in the metal heater 410, the upper metal plate 411, the heater412 and the lower metal plate 421 are secured through the metal platefixing screws 417. Here, the metal plate fixing screws 417 are attachedin a manner so as to penetrate the heater 412 and the lower metal plate421 and so as not to penetrate the upper metal plate 411.

As described above, in the case where the upper metal plate 411 and thelike are secured through the metal plate securing screws 417, the lengthof the portion of each metal plate securing screw 417 inserted into theupper metal plate 411 is desirably set to ¾ or less of the thickness ofthe upper metal plate.

When the length of the portion of each metal plate securing screw 417inserted into the upper metal plate 411 is longer than ¾ of thethickness of the upper metal plate 411, the temperature of a portionright above each metal plate securing screw 417 of the heating face ofthe metal plate becomes higher in comparison with the temperature of itsperipheral portion, failing to evenly heat an object to be heated.

Moreover, the metal heater 410 has a structure in which the screw headof each metal plate securing screw 417 is embedded in the lower metalplate 421. Therefore, the upper metal plate 411, the heater 412 and thelower metal plate 421 can be firmly secured inside the supporting case420 more positively so that the upper metal plate 411 is allowed to havea structure that is less likely to result in a deformation such aswarping, sagging and the like.

The heater 412 has a circular shape in its plan view in the same manneras the upper metal plate 411 and the lower metal plate 421, and theheating element 425, constituted by closed circuits, is arranged in theheater 412 so as to heat the entire heating face 411 a of the uppermetal plate 411 to an even temperature. With respect to the heatingelement 425, as shown in FIG. 2, a heating element, of a pattern inwhich a winding line is repeatedly placed in a ring shape on theperiphery of a heater to form a closed circuit, and a heating element,of a pattern in which a winding line is repeatedly placed inside thereofin a manner so as to form a part of a concentric circle to form a closedcircuit, are arranged.

Moreover, although not shown in the figures, the heater 412 has astructure in which the heating element 425 is sandwiched by two micaplates and secured therein, and upon current application, the heatingelement 425 heats the mica plates so that an object to be heated isheated by secondary radiation from the mica plates.

In the metal heater 410 of the first aspect of the present invention,the peripheral edge of the heating element 425 formed inside the heater412 is desirably located at a position within 25% of the diameter of themetal plate 411 from the periphery of the metal plate 411. Normally, thetemperature on the peripheral portion of the metal plate 411 tends tobecome uneven due to heat radiation from the surface of the peripheralportion of the metal plate 411; however, in the metal heater 410according to the first aspect of the present invention, since theheating element is also disposed at the peripheral portion, asemiconductor wafer or the like, that is, the object to be heated can beevenly heated without dispersion in temperature.

With respect to the material, shape and the like of the metal heaterforming the first aspect of the present invention and the manufacturingmethod of the metal heater according to the first aspect of the presentinvention, detailed description will be given later.

In the following, description will be given of an embodiment accordingto the second aspect of the present invention.

The metal heater according to the second aspect of the present inventionis a metal heater comprising a plurality of metal plates and a heatingelement, the heating element sandwiched between the metal plates.Herein, the plurality of metal plates are made of the same material.Referring to the drawings, description will be given of a metal heaterin which a heater is sandwiched between two metal plates as one exampleof the metal heater according to the second aspect of the presentinvention.

FIG. 5(a) is a cross-sectional view that schematically shows such ametal heater, and FIG. 5(b) schematically shows a method by which aheating element and a conductive line are joined to each other bycaulking using a joining foil in the metal heater shown in FIG. 5(a).

In this metal heater 510, a heater 512 is sandwiched between an uppermetal plate 511 and a lower metal plate 521, each of which has a diskshape, and the upper metal plate 511, the heater 512 and the lower metalplate 521 are fixedly secured to, and tightly bound to one anotherthrough metal plate securing screws 517 so that heat from the heater 512is suitably transmitted to the upper metal plate 511.

Moreover, the thickness of the upper metal plate 511 is made larger thanthe thickness of the lower metal plate 521. Therefore, as has beendescribed already, the flatness of the heating face is maintained, andthe temperature of the heating face is made even so that the object tobe heated can be evenly heated.

By securing the metal plate using the metal plate securing screws 517,the thickness of the metal plate becomes substantially large so that theflatness of the heating face is further improved.

The upper metal plate 511, the heater 512 and the lower metal plate 521,fixedly secured to one another through the metal plate securing screws517 are supported by a supporting plate 525 placed on the bottom face ofa supporting case 520 having a cylinder shape with a bottom, and in thisstructure, portions other than the contact portion to the supportingplate 525 do not contact with the supporting case 520. Moreover, a heatshielding plate 523 for shielding heat is provided below the supportingcase 520. Moreover, a barrier ring 532 is placed on the peripheral edgeof the supporting case 520. By providing the barrier ring, it becomespossible to prevent outside gases from flowing therein, and consequentlyto prevent temperature change in the heating face 511 a.

With the above-mentioned structure, the metal heater 510 according tothe second aspect of the present invention makes it possible to realizea flatness of 50 μm or less on the heating face 511 a of the upper metalplate 511. By realizing such a flatness, upon heating a semiconductorwafer, the distance between the semiconductor wafer and the metal platecan be made almost constant so that the entire semiconductor wafer canbe heated to an even temperature.

The metal heater 510 according to the second aspect of the presentinvention may be provided with a wafer guide ring 526 on the peripheraledge portion of the heating face 511 a so as to prevent temperaturechange due to a gas flowing therein from outside.

In the metal heater 510 according to the second aspect of the presentinvention, the side faces of the upper metal plate 511, the heater 512and the lower metal plate 521 are not made in tightly contact with thesupporting case 520, and secured in a non-contact state, and the lowermetal plate 521 also does not directly contact with the bottom face ofthe supporting case 520, and is supported by a supporting plate 525.With this arrangement in which the side faces of the upper metal plate511, the heater 512 and the lower metal plate 521 are not made incontact with the supporting case 520, the upper metal plate 511 can beprevented from being curved due to pressure from the side faces when theupper metal plate 511 has been thermally expanded. Moreover, the uppermetal plate 511, the heater 512 and the lower metal plate 521 aresupported only through the supporting plate 525, without contacting withany other portions; thus, upon heating an object to be heated, heatreleased from the metal plate and the like is reduced so that an objectto be heated can be heated more quickly in comparison with the case inwhich the side faces of the upper metal plate 511, the heater 512 andthe lower metal plate 521 are made in tightly contact with thesupporting case 520. In this case, an air layer is allowed to functionas a heat insulating layer.

Here, the upper metal plate 511, the heater 512, the upper metal plate521 and the like, as they are, may be placed on the bottom face of thesupporting case 520, without providing the supporting member 525 on thebottom face of the supporting case 520.

After the heating process, the upper metal plate 511, the heater 512 andthe lower metal plate 521 sometimes need to be cooled quickly, and insuch a case, for example, a cooling pipe or the like is connected to thebottom plate of the supporting case 520, with cooled air or the likeintroduced into the supporting case 520, so that it becomes possible tocarry out a quick cooling process.

Moreover, the metal heater 510 has a structure in which the metal platesecuring screws 517 do not penetrate supporting case 520, and areallowed to penetrate only the upper metal plate 511, the heater 512 andthe lower metal plate 521, and designed to secure these members. Withthis structure, it becomes possible to prevent deformation in the uppermetal plate 511 due to a difference in thermal expansion coefficientsbetween the upper metal plate 511 and the supporting case 520, and alsoto reduce heat released from the upper metal plate 511 and the like uponheating an object to be heated so that the object to be heated can beheated quickly.

A heat shielding plate 523 is placed on the bottom portion of thesupporting case 520 so that it becomes possible to prevent heat,released from the upper metal plate 511 and the lower metal plate 521,from transferring to the device.

Moreover, a bottomed hole 514 is formed in the metal heater 510, and atemperature measuring element 516 used for measuring the temperature ofthe upper metal plate 511 is embedded in the bottomed hole 514.

Here, in the metal heater 510, supporting pins 518, each having apinnacle-like tip, are placed on the heating face, and the semiconductorwafer 519 is supported through the supporting pins 518 so that thesemiconductor wafer 519 can be supported with a fixed distance kept fromthe heating face of the upper metal plate 511, so as to be heated.

In the metal heater according to the second aspect of the presentinvention, with respect to the number of the supporting pins, althoughnot particularly limited, it is desirably six or more in the case where,for example, the diameter of the metal plate is 12 inches (300 mm) ormore. The reason therefor is the same as that described in the metalheater according to the first aspect of the present invention.

Moreover, the metal heater 510 is provided with through holes 515 eachof which penetrates the upper metal plate 511, the heater 512, the lowermetal plate 521 and the supporting case 520, and by insertingpillar-shaped lifter pins and the like through the through holes 515, asemiconductor wafer 519, that is, the object to be heated is supportedwith a fixed distance kept from the heating face 51 a of the upper metalplate 511 so that the semiconductor wafer 519 can be properlytransported.

Here, the heater 512 is connected to a conductive line 524, and theconductive line 524 is led outside from a through hole formed in thesupporting case 520 and the heat shielding plate 523, and connected to apower supply or the like (not shown).

In the metal heater 510 shown in FIG. 5, the through hole is formed inthe lower metal plate 521, and the conductive line 524 is inserted intothe through hole; however, the conductive line 524 may be connected to aheating element placed inside the heater on the side face of the heater512.

Moreover, in the metal heater 510, the upper metal plate 511, the heater512 and the lower metal plate 521 are fixedly secured by the metal platesecuring screws 517. Here, the metal plate securing screws 517 areattached in a manner so as to penetrate the heater 512 and the lowermetal plate 521, and so as not to penetrate the upper metal plate 511.

As described above, in the case where the upper metal plate 511 and thelike are secured through the metal plate securing screws 517, the lengthof the portion of each metal plate securing screw 517 inserted into theupper metal plate 511 is desirably ¾ or less of the thickness of theupper metal plate.

When the length of the portion of each metal plate securing screw 517inserted into the upper metal plate 511 is longer than ¾ of thethickness of the upper metal plate 511, the temperature of a portionright above each metal plate securing screw 517 of the heating face ofthe metal plate becomes higher than the temperature of its peripheralportion, failing to evenly heat an object to be heated.

The heater 512 has a circular shape in its plan view in the same manneras the upper metal plate 511 and the lower metal plate 521, and theheating element 525, constituted by closed circuits, is arranged in theheater 512 so as to heat the entire heating face 511 a of the uppermetal plate 511 to an even temperature.

In the heater 512, as shown in FIG. 2, a heating element, of a patternin which a winding line is repeatedly placed in a ring shape on theperiphery of the heater 512 to form a closed circuit, and a heatingelement, of a pattern in which a winding line is repeatedly placedinside thereof in a manner so as to form a part of a concentric circleto form a closed circuit, are arranged.

Moreover, although not shown in the figures, the heater 512 has astructure in which the heating element is sandwiched between two micaplates and secured therein, and upon current application, the heatingelement heats the mica plates so that an object to be heated can beheated by secondary radiation from the mica plates. The heating elementmay be formed by a stainless foil.

In the metal heater 510 according to the second aspect of the presentinvention, the peripheral edge of the heating element formed inside theheater 512 is desirably located at a position within 25% of the diameterof the metal plate 511 from the periphery of the metal plate 511.Normally, the temperature on the peripheral portion of the metal plate511 tends to become uneven due to heat radiation from the surface of theperipheral portion of the metal plate 511; however, in the metal heater510 according to the second aspect of the present invention, since theheating element is also disposed at the peripheral portion, asemiconductor wafer or the like, that is, the object to be heated can beevenly heated without dispersion in temperature.

With respect to the material, shape and the like of the metal heaterforming the second aspect of the present invention and the manufacturingmethod of the metal heater according to the second aspect of the presentinvention, detailed description will be given later.

In the following, description will be given of an embodiment accordingto the third aspect of the present invention.

The metal heater according to the third aspect of the present inventionis a metal heater comprising a plurality of metal plates and a heatingelement, with the heating element sandwiched between the metal plates.Herein, a convex portion for supporting an object to be heated is placedon a heating face opposing the object to be heated of the metal platecorresponding to an area on which the heating element is formed.

Referring to the drawings, description will be given of a metal heaterin which a heater is sandwiched between two metal plates as one exampleof the metal heater according to the third aspect of the presentinvention.

FIG. 6(a) is a cross-sectional view that schematically shows such ametal heater, and FIG. 6(b) schematically shows a method by which aheating element and a conductive line are joined to each other bycaulking using a joining foil in the metal heater shown in FIG. 6(a).Moreover, FIG. 7 is a plan view that shows the metal heater of FIG.6(a). Here, in FIG. 7, the heating element is indicated by a brokenline.

In a metal heater 610, each of supporting pins 618 having a tip portionlike a nail is inserted into each of concave portions 628 prepared ascylinder shaped hollow sections formed on the upper metal plate 611, anda C-shaped spring 627 is fitted to each concave portion 628 so as tocontact therewith in a manner so as to enclose the supporting pin 618 sothat the supporting pin 618 is fixedly secured to the heating face 611 aof the upper metal plate 611.

Here, in the present embodiment, the supporting pin is placed on theheating face of the metal plate by using a means shown in FIG. 6;however, with respect to the means for placing the supporting pin on theheating face of the metal plate, not limited to the means shown in FIG.6, for example, a method in which a supporting pin having a screwportion is engaged with a concave portion in which thread grooves areformed.

Moreover, as shown in FIG. 2, on the heating face 611 a of the uppermetal plate 611, eight supporting pins 618 are placed on circumferencesof concentric circles of the upper metal plate 611 and one supportingpin 618 is placed on the center portion of the upper metal plate 611 atan area located on a comparatively peripheral portion of the upper metalplate 611; thus, the total nine supporting pins 618 are placed thereon.Here, the supporting pins located on the same circumference are placedso as to have the same interval, in order to prevent sagging in thesemiconductor wafer 619.

Here, the other structures are the same as those of the metal heater 510according to the second aspect of the present invention shown in FIG. 5;therefore, the description thereof is omitted.

The metal heater 610 according to the third aspect of the presentinvention, which has the above-mentioned structure, makes it possible torealize a flatness of 50 μm or less on the heating face 611 a of theupper metal plate 611. By realizing such a flatness, upon heating asemiconductor wafer, the distance between the semiconductor wafer andthe metal plate is made almost constant so that the entire semiconductorwafer can be heated to have an even temperature.

The metal heater 610 according to the third aspect of the presentinvention may be provided with a wafer guide ring 626 on the peripheraledge portion of the heating face 611 a so as to prevent temperaturechanges due to a gas flowing therein from outside, or may be providedwith a barrier ring 632 thereon.

The metal heater 610 according to the third aspect of the presentinvention is different from a conventional metal heater 450 shown inFIGS. 4(a) and 4(b) in the following points.

First, as described above, the metal heater 610 has the structure inwhich the total nine supporting pins 618 are placed on the heating face611 a of the upper metal plate 611, while the metal heater 450 has astructure in which the total five supporting pins 458 are placed on theheating face 451 a of the metal plate 451; thus, the numbers of thesupporting pins are different from each other. Therefore, since themetal heater 610 has a narrower gap between the supporting pins 618, itbecomes possible to make the semiconductor wafer 619 less likely tosagging. For this reason, the distance between the semiconductor wafer619 and the heating face 611 a of the upper metal plate 611 is madealmost constant so that the heating process can be carried out on theentire semiconductor wafer 619 evenly.

Moreover, in the metal heater 610, the side faces of the upper metalplate 611, the heater 612 and the lower metal plate 621 are not made intightly contact with the supporting case 620, and secured in anon-contact state, and the lower metal plate 621 is not made in directcontact with the bottom face of the supporting case 620 either, andsupported by a supporting plate 625. With this structure in which theside faces of the upper metal plate 611, the heater 612 and the lowermetal plate 621 are kept in a non-contact state with the supporting case620, the upper metal plate 611 can be prevented from being curved due topressure from the side faces when the upper metal plate 611 has beenthermally expanded. In the case of the structure in which the uppermetal plate 611, the heater 612 and the lower metal plate 621 aresupported only through the supporting plate 625, with no other portionsmade in contact therewith, upon heating an object to be heated, heatreleased from the metal plate and the like is reduced so that an objectto be heated can be heated more quickly in comparison with the case inwhich the side faces of the upper metal plate 611, the heater 612 andthe lower metal plate 621 are made in tightly contact with thesupporting case 620. In this case, an air layer is allowed to functionas a heat insulating layer.

Here, the upper metal plate 611, the heater 612 and the lower metalplate 621, as they are, may be placed on the bottom face of thesupporting case 620, without providing the supporting member 625 on thebottom face of the supporting case 620.

After the heating process, the upper metal plate 611, the heater 612 andthe lower metal plate 621 sometimes need to be cooled quickly, and insuch a case, for example, a cooling pipe or the like is connected to thebottom plate of the supporting case 620, with cooled air or the likeintroduced into the supporting case 620, so that it becomes possible tocarry out a quick cooling process.

Moreover, the metal heater 610 has a structure in which the metal platesecuring screws 617 do not penetrate the supporting case 620, and areallowed to penetrate only the upper metal plate 611, the heater 612 andthe lower metal plate 621, and designed to secure these members. Withthis structure, it becomes possible to prevent deformation in the uppermetal plate 611 due to a difference in thermal expansion coefficientsbetween the upper metal plate 611 and the supporting case 620, and alsoto reduce heat released from the upper metal plate 611 and the like uponheating an object to be heated so that the object to be heated can beheated quickly.

In the metal heater 610 according to the third aspect of the presentinvention, the peripheral edge of the heating element 625 formed insidethe heater 612 is desirably located at a position within 25% of thediameter of the metal plate 611 from the periphery of the metal plate611. The reason therefor is the same as described in the first aspect ofthe present invention.

With respect to the material, shape and the like of the metal heaterforming the third aspect of the present invention and the manufacturingmethod of the metal heater according to the third aspect of the presentinvention, detailed description will be given later.

In the following, description will be given of the materials, shapes andthe like of the metal heaters according to the first to third aspects ofthe present invention. Here, since the materials, shapes and the like ofthe metal heaters according to the first to third aspects of the presentinvention are almost the same, the description thereof will be given alltogether.

With respect to each of the metal heaters according to the first tothird aspects of the present invention, the metal plate is provided withbottomed holes formed on the side opposite to the heating face side onwhich an object to be heated is placed, toward the heating face, and thebottom of each bottomed hole is formed relatively closer to the heatingface from the heating element, and a temperature measuring element (notshown), such as a thermocouple or the like is desirably provided on thebottomed hole.

Moreover, the distance between the bottom of the bottomed hole and theheating face is desirably between 0.1 mm and ½ of the thickness of themetal plate. Thus, the temperature measuring place is made closer to theheating face from the heating element so that it becomes possible tomeasure the temperature of the semiconductor wafer more accurately.

The distance between the bottom of the bottomed hole and the heatingface of less than 0.1 mm causes heat radiation, resulting in adistribution of temperature on the heating face; in contrast, thedistance exceeding ½ of the thickness makes the metal plate more likelyto be influenced from the temperature of the heating element, resultingin a failure in temperature control, and the subsequent distribution oftemperature on the heating face.

The diameter of the bottomed hole is desirably 0.3 to 5 mm. The reasontherefor is because, when the diameter is too large, the heat radiatingproperty becomes too high, while, when the diameter is too small, themachining property becomes too low; thus, it becomes impossible toevenly maintain the distance from the heating face.

With respect to the temperature measuring element, for example, athermocouple, a platinum temperature measuring resistor, a thermistorand the like may be used. With respect to the thermocouple, for example,as listed in JIS-C-1602 (1980), K-type, R-type, B-type, S-type, E-type,J-type and T-type thermocouples may be used. Among these, the K-typethermocouples are more desirably used.

The size of the coupling portion of the thermocouple is set to the sameas the diameter of an element wire, or greater than the diameterthereof, and is desirably 0.5 mm or less. The coupling portion that isgreater than this tends to cause a great thermal capacity and thesubsequent reduction in responsivity. Here, it is difficult to make thecoupling portion smaller than the diameter of an element wire.

The temperature measuring element may be bonded to the bottom of thebottomed hole by using gold alloy, silver alloy or the like, or may besealed with a heat resistant resin after having been inserted into thebottomed hole, or both of the above-mentioned methods may be used incombination.

With respect to the heat resistant resin, examples thereof includethermosetting resins, in particular, epoxy resin, polyimide resin,bismaleimide-triazine resin and the like. Each of these resins may beused alone, or two or more resins of these may be used in combination.

With respect to the gold alloy, at least one kind selected from thegroup consisting of Au (37 to 80.5% by weight)—Cu (63 to 19.5% byweight) alloy and Au (81.5 to 82.5% by weight)—Ni (18.5 to 17.5% byweight) alloy is desirably used. These alloys have melting temperaturesof 900° C. or more, and hardly melt even at a high-temperature range.

With respect to the silver alloy, for example, Ag—Cu-based alloys may beused.

With respect to the heater, a mica heater as shown in FIG. 2, a siliconrubber heater or the like may be used. Moreover, a heater in which aheating element line is simply formed on an insulating seal may also beused.

With respect to the mica heater, a heater in which a heating elementsuch as a nichrome wire or the like, formed into an optional pattern, issandwiched by mica plates serving as insulating members may be used.Moreover, with respect to the silicon rubber heater, a heater in which aheating element such as a nichrome wire or the like, formed into anoptional pattern, is sandwiched by silicon rubber plates serving asinsulating members may be used.

With respect to the heating element to heat the heater, not limited bythe above-mentioned nichrome wire, another metal line, such as atungsten line, a molybdenum line and the like, and the like may be usedas long as it generates heat upon applying a voltage.

Moreover, with respect to the heating element, in addition to the metalline, metal foil may be used. With respect to the metal foil, a heatingelement in which nickel foil, stainless foil or the like is etched intoa pattern is desirably used. The patterned metal foils may be bonded toeach other by using a resin film or the like.

With respect to the insulating member used for coating the heatingelement, not limited to the above-mentioned mica plate and siliconrubber, for example, a material, such as fluororesin, polyimide resin,polybenzoimidazole (PBI) or the like, may be used as long as it iscapable of preventing short-circuiting and of withstanding hightemperatures, and a material in which fibers made from ceramics or thelike are formed into a mat shape may also be used.

In the case where the metal heater has a structure in which the heateris sandwiched between metal plates, a plurality of the heaters may beprovided. In this case, with respect to the patterns of the respectivelayers, heating elements are desirably formed in any of the layers so asto compensate for one another, and the pattern is desirably formed inany of areas, when viewed from above the heating face. Examples of sucha structure include a staggered structure.

Moreover, with respect to the pattern of the heating element in themetal heaters according to the first to third aspects of the presentinvention, not limited to the pattern as shown in FIG. 2 and the like,for example, patterns, such as a concentric circle pattern, a spiralpattern, an eccentric circular pattern and the like, maybe used.Moreover, a combined pattern of them may be used.

The heating element is desirably divided into two or more parts, asdescribed above.

Moreover, the area resistivity of the heating element is desirably 0.1to 10Ω/

. When the area resistivity exceeds 10Ω/

, the diameter of the heating element needs to be made extremely smallerin order to ensure a desired quantity of heat generation, and, for thisreason, even a slight chip or the like tends to cause disconnection ordispersion in resistance value. Moreover, in the case where the arearesistivity is less than 0.1Ω/

, the diameter of the heating element needs to be made larger so as toensure a sufficient quantity of heat generation; thus, the degree offreedom in designing the pattern of the heating element is lowered, andit becomes difficult to evenly control the temperature of the heatingface.

With respect to the means for connecting the heating element to a powersupply, as shown in FIG. 1, a part of the heating element made of metalfoil is exposed to form a connecting foil, and one end of the conductiveline is wrapped with the connecting foil, with an attaching memberhaving a caulking portion attached to this portion, so that theconnection is made by caulking the caulking portion, or conductive linesmay be attached to the both ends of the heating element throughsoldering or the like so that the connection to the power supply or thelike may be made through these conductive lines, or terminals may beattached to the two ends of the heating element so that the connectionto the power supply or the like may be made through these terminals.

Here, the terminals are desirably attached to the heating elementthrough soldering, brazing, crimping, caulking or the like. Theterminals are desirably attached through soldering because nickelprevents thermal diffusion of solder. With respect to the connectingterminals, for example, external terminals made of Kovar may be used.

With respect to the solder used for connecting the connecting terminals,an alloy, such as a silver-lead alloy, a lead-tin alloy, a bismuth-tinalloy and the like, may be used. The thickness of the solder layer ispreferably 0.1 to 50 μm. This range makes it possible to sufficientlyensure connection through soldering.

Moreover, in the metal heater according to the first to third aspects ofthe present invention, an intermediate plate may be interposed betweenthe metal plate and the heater. By interposing such an intermediateplate, heat generated by the heating element can be transmitted to themetal plate in a further even state.

With respect to the material of the intermediate plate, ametal having asuperior thermal conductivity is desirably used, and, for example,copper, a copper alloy or the like may be used.

In the metal heater shown in FIG. 1, the side face of the metal plateand the supporting case are in a non-contact state; however, in the casewhere these members are made in contact with each other, a heatinsulating ring is desirably interposed between the side face of themetal plate and the supporting case. Since heat is released from theperipheral portion of the metal plate, it becomes possible to preventtemperature dispersion from occurring on the heating face of the metalplate.

The supporting case and the heat shielding plate may be integrallyformed, or the heat shielding plate may be coupled and secured to thesupporting case. Desirably, the supporting case and the heat shieldingplate are integrally formed. Thus, it becomes possible to ensure thestrength of the entire metal heater.

The supporting case desirably has a cylinder shape, and the heatshielding plate desirably has a disk shape. Moreover, the thickness ofthe supporting case and that of the heat shielding plate are desirably0.1 to 5 mm. The thickness of less than 0.1 mm causes insufficientstrength, and the thickness exceeding 5 mm makes the thermal capacitygreater.

The supporting case and the heat shielding plate are desirably made of ametal, such as SUS, aluminum, inconel (nickel-based alloy containing 16%of chrome and 7% of iron) or the like, so as to allow easy machining andsuperior mechanical properties and ensure sufficient strength in theentire metal heater.

In the case where the supporting case and the heat shielding plate arenot prepared as an integral part, the heat shielding plate may be madeof a material, such as a heat resistant resin, a ceramic plate, acomposite plate formed by blending heat-resistant organic fibers andinorganic fibers into these materials, or the like, that has a thermalconductivity that is not so high, and is superior in heat resistance, soas to achieve a superior heat shielding property.

Moreover, a coolant introducing pipe may be attached to the supportingcase or the heat shielding plate. By introducing a coolant or the likeused for forcibly cooling the metal heater, the metal heater can bequickly cooled. Moreover, a through hole for discharging the introducedcoolant or the like for forcible cooling may be formed in the supportingcase or the heat shielding plate.

In the following, description will be given of a manufacturing method ofthe metal heaters according to the first to third aspects of the presentinvention.

(1) Manufacturing Processes of Metal Plate

A plate-shaped member, made of a material such as an aluminum-copperalloy or the like, is machined at outer diameter portion by using an NClathe and formed into a disk shape, and this plate-shaped member is thensubjected to an end-face machining process, a surface machining processand a rear-face machining process in succession.

In this case, the thickness of the plate-shaped member to form an uppermetal plate is made larger than the thickness of a plate-shaped memberto form a lower metal plate.

Next, each of parts to be through holes into which lifter pins forsupporting a semiconductor wafer are inserted, each of concave portionson which supporting pins are placed and each of parts to be bottomedholes in which a temperature measuring element, such as a thermocouple,is embedded are formed by using a machining center (MC) or the like.Moreover, after bottomed holes have been formed at predeterminedpositions, thread grooves are formed in the bottomed holes so that screwholes through which metal plate securing screws are inserted are formed.

In particular, in the case where the metal heater according to the thirdaspect of the present invention is manufactured, the concave portionsfor placing the supporting pins are formed in a manner so as to widelyspread the supporting pins on the metal plate as well as place them withequal intervals. With respect to the layout thereof, for example, asshown in FIG. 7, a plurality of supporting pins 618 are placed oncircumferences of concentric circles of the metal plate at equalintervals, with a single supporting pin 618 placed in the center portionof the metal plate. With this arrangement, upon heating thesemiconductor wafer, the semiconductor wafer is made free from saggingso that the distance of a semiconductor wafer and a metal plate is madeeven; thus, the semiconductor wafer can be evenly heated.

Moreover, the plate-shaped member to form the upper metal plate issubjected to a surface grinding process by using a rotary grindingmachine so that the upper metal plate and the lower metal plate aremanufactured. By carrying out this surface grinding process, theflatness of the surface of the metal plate can be set to about 20 to 30μm.

Furthermore, a wafer guide ring for suppressing an ambient gas (forexample, air or the like) flow may be formed on the upper metal plate,if necessary. The above-mentioned wafer guide ring maybe made of, forexample, an aluminum-copper alloy, SUS or the like. Moreover, a barrierring may be formed on the uppermost portion of the supporting case forthe same purpose.

By providing the wafer guide ring and the barrier ring, the ambient gasflows inside and outside the heating area are intervened so that theobject to be heated can be evenly heated.

Next, the upper metal plate and the lower metal plate are subjected toan alumite treatment so that oxide coat films are formed on the surfacesof the upper metal plate and the lower metal plate. By carrying out thistreatment, the corrosion resistance of the metal plate is improved witha harder surface; therefore, the metal plate becomes less likely to havescratches or the like. Moreover, even when the metal plate is usedduring actual semiconductor producing and examining processes, the metalplate becomes less likely to receive corrosion due to a resist solution,corrosive gases and the like.

With respect to the alumite treatment (anode oxidation coatingtreatment), for example, a sulfate method, an oxalate method or the likemay be used, and the oxalate method is desirably used. Thus, it becomespossible to prevent surface pinholes from occurring after thetreatments.

(2) Placement of Heater

A heater, formed by sandwiching a heating element such as a nichromewire processed into a predetermined pattern, a metal foil like astainless foil, or the like between ceramic plates such as mica platesor the like, is placed between the upper metal plate and the lower metalplate, and after metal plate securing screws have been inserted throughscrew holes formed in the lower metal plate and the heater, the lowermetal plate and the heater are fastened into an integral part bytightening the screws.

Here, since the entire heater needs to be set to an even temperature inthe heating element, a pattern or the like which is basically formed byrepeatedly placing a winding line in a ring shape or repeatedly drawinga winding line in a manner so as to form a part of each of concentriccircles is preferably used.

Moreover, an intermediate plate, made of a material having superiorthermal conductivity such as copper or the like, may be sandwichedbetween the metal plate and the heater. With this arrangement, heatradiated from the heater can be transmitted to the upper metal plate ina further even state.

(3) Attachment of Supporting Case

A device in which the metal plate and the heater are integrally formedin this manner is supported in a cylinder-shaped supporting case shownin FIG. 1 and secured therein.

A heat shielding plate, made from the same material as the supportingcase, is placed on the bottom face of the supporting case, and throughholes, which allow a temperature measuring element, a conductive lineand the like to pass, are formed in the supporting case.

In the metal heaters according to the first to third aspects of thepresent invention, as shown in FIG. 1, the side faces of the metal plateand the heater are desirably supported and secured in the supportingcase in a non-contact state therewith.

This structure is prepared because the peripheral portion of the heatingface of the metal plate tends to have a low temperature due to releasedheat from the side faces of the metal plate and the heater.

In the case where the side faces of the metal plate and the heater aresupported and secured in the supporting case in a contact statetherewith, a heat insulating ring made of polyimide resin, fluororesinor the like is desirably interposed between the metal plate and thesupporting case.

(4) Connection to Power Supply or the Like

Terminals (external terminals) for use in connection to a power supplyare attached to both ends of the heating element provided in the heaterthrough a brazing material or solder, or by using a mechanical attachingmethod (attaching means) such as crimp screwing, caulking or the like,so that the heater is connected to an external power supply or the like;thus, the manufacturing processes of the metal heater are completed.Here, in the case where the metal heater according to the third aspectof the present invention is manufactured, after supporting pins formedon the heating face of the metal plate have been inserted, thesupporting pins are secured by using springs or the like to complete themanufacturing processes of the metal heater.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, description will be given of the first to thirdaspects of the present invention by way of examples in detail.

The following examples exemplify a case in which a metal heater forheating a semiconductor wafer is used; however, the first to thirdaspects of the present invention may be applied to a heater fortemperature adjustment for an optical waveguide.

EXAMPLE 1

Manufacturing of metal heater (see FIGS. 1 and 2)

(1) A plate-shaped member, made of an aluminum-copper alloy (A2219(JIS-H4000)), was machined at outer-diameter portion by using an NClathe (manufactured by Washino Machinery Co., Ltd.) and formed into adisk shape, and this plate-shaped member was then subjected to anend-face machining process, a surface machining process and a rear-facemachining process so that a disk-shaped member for an upper metal plateand a disk-shaped member for a lower metal plate were manufactured.

Next, each of parts to be through holes 415 to which lifter pins usedfor supporting a semiconductor wafer 419 are inserted, each of concaveportions in which supporting pins 418 are placed and each of parts to bea bottomed hole 414 in which a temperature measuring element 416 isembedded were formed by using a machining center (Hitachi Seiki Co.,Ltd.).

Here, the through holes 415 were formed at three positions, and theconcave portions for placing the supporting pins 418 were formed at ninepositions.

After the bottomed holes or the through holes had been formed atpredetermined positions in the same manner, thread grooves were formedin the bottomed holes or the through holes so that screw holes throughwhich metal plate securing screws 17 are inserted were formed in thedisk shape.

Here, the screw holes were formed in the upper metal plate and theplate-shaped member with a depth of ¾ of the thickness thereof.

(2) Next, the disk member for the upper metal plate, manufacturedthrough the processes of (1), was subjected to a surface grindingprocess on its surface on the heating face side by using a rotarygrinding machine (manufactured by Okamoto Machine Tool Works, Ltd.) sothat an upper metal plate 411 having a thickness of 15 mm and a diameterof 330 mm and a lower metal plate 421 having a thickness of 5 mm and adiameter of 330 mm were obtained.

Moreover, a barrier ring 428 for suppressing a gas flow toward asemiconductor wafer that is an object to be heated was placed on a sideface of the upper metal plate 411 by using the above-mentioned method.

In other words, the peripheral edge portion of the supporting case wasmade higher than the upper face (heating face) of the upper metal plateso that the barrier ring was formed.

Here, in this example, the thickness of the upper metal plate 411 wasmade larger than the thickness of the lower metal plate 421.

(3) Next, the upper metal plate 411 and the lower metal plate 421 weresubjected to an alumite treatment under conditions of 10% H₂SO₄electrolytic solution, a voltage of 10 V, a current density of 0.8 A/dm²and a liquid temperature of 20° C. so that an oxide coat film having athickness of 15 μm was formed on each of the surfaces of the upper metalplate 411 and the lower metal plate 421.

(4) A heating element 425, made of a stainless foil having a thicknessof 200 μm on which a winding wire shown in FIG. 2 is placed in arepeated pattern to form a ring shape and a winding wire is repeatedlyplaced in a pattern so as to form a part of each of concentric circles,was sandwiched between two mica plates 426 having a thickness of 0.3 mmto obtain a heater 412 having a diameter of 330 mm.

Here, in the heater 412, the heating element 425 was formed so that theouter rim of the heating element was placed at a position within 25% ofthe diameter of the upper metal plate 411 from the periphery of theupper metal plate 411, and the total number of the circuits of theheating element 425 was set to four.

Moreover, parts to be through holes 415, a part to be the bottomed hole414 and parts to be screw holes through which metal plate securingscrews 417 are inserted were preliminary formed in the mica plate 426.

Thereafter, the heater 12 was sandwiched between the upper metal plate411 and the lower metal plate 421 manufactured through the processes of(1) to (3), and after the metal plate securing screws 417 had beeninserted through the screw holes formed in the lower metal plate 421 andthe heater 412, the securing screws were tightened so that the uppermetal plate 411, the lower metal plate 421 and the heater 412 werecombined into an integral part.

(5) Next, a supporting case 420 having a cylinder shape as shown in FIG.1, made of SUS, was manufactured, and after parts to be the throughholes 415, a part to be the bottomed hole 414 and a through hole throughwhich the conductive wire 424 is inserted had been formed in the bottomface of the supporting case 420, a heat shielding plate 423 having adisk shape, made of SUS, was placed on the bottom portion of thesupporting case 420.

Moreover, the upper metal plate 411 to which the heater 412 and thelower metal plate 421 had been attached, manufactured in the process(4), was placed inside the supporting case 420 in which the heatshielding plate 423 had been placed, and fixedly secured therein so thatthe side faces of the upper metal plate 411, the heater 412 and thelower metal plate 621 were kept in no-contact with the supporting case420.

Here, in the metal heater in this example, the screw head of each metalplate securing screw 417 was designed to be embedded into the lowermetal plate 421 so that the bottom face of the lower metal plate 421 wasmade in contact with the inner face of the supporting case 420.

(6) After a temperature measuring element 416 made of a platinumtemperature measuring resistor for use in controlling temperatures hadbeen inserted into the bottomed hole 414, the bottomed hole 414 wassealed by using an inorganic adhesive (Aron ceramic, made by ToagoseiCo., Ltd.) . Moreover, supporting pins 418 were placed in the concaveportions formed on the heating face of the upper metal plate 411.

(7) Next, the conductive wire 424 was wrapped by a connecting foil takenout of the stainless foil serving as the heating element provided in theheater 412, and a metallic attaching member was attached thereto, andthis was then caulked so that the connecting foil and the conductivewire 424 were connected to each other and secured with each other. Thus,the heating element provided in the heater 412 was connected to anexternal power supply or the like so that a metal heater 410 wasobtained.

EXAMPLE 2

Manufacturing of Metal Heater

The same processes as those of Example 1 were carried out except thatthe thickness of the upper metal plate 411 was set to 20 mm and that thethickness of the lower metal plate 421 was set to 5 mm so that a metalheater was manufactured.

EXAMPLE 3

Manufacturing of Metal Heater

The same processes as those of Example 1 were carried out except thatthe thickness of the upper metal plate 411 was set to 25 mm and that thethickness of the lower metal plate 421 was set to 10 mm so that a metalheater was manufactured.

EXAMPLE 4

Manufacturing of Metal Heater

The same processes as those of Example 1 were carried out except thatthe thickness of the upper metal plate 411 was set to 40 mm and that thethickness of the lower metal plate 421 was set to 5 mm so that a metalheater was manufactured.

EXAMPLE 5

The same processes as those of Example 1 were carried out except thatthe thickness of the upper metal plate 411 was set to 20 mm and that thethickness of the lower metal plate 421 was set to 20 mm so that a metalheater was manufactured.

EXAMPLE 6

The same processes as those of Example 1 were carried out except thatthe thickness of the upper metal plate 411 was set to 36 mm and that thethickness of the lower metal plate 421 was set to 3 mm so that a metalheater was manufactured.

EXAMPLE 7

The same processes as those of Example 1 were carried out except thatthe thickness of the upper metal plate 411 was set to 50 mm and that thethickness of the lower metal plate 421 was set to 5 mm so that a metalheater was manufactured.

TEST EXAMPLE 1

The same processes as those of Example 1 were carried out except that inthe processes of (1) to (3) in Example 1, the thickness of the uppermetal plate was set to 5 mm and that the thickness of the lower metalplate was set to 20 mm so that a metal heater was manufactured. In thistest example, the thickness of the lower metal plate was made largerthan the thickness of the upper metal plate.

TEST EXAMPLE 2

The same processes as those of Example 1 were carried out except that inthe process of (5) of Example 1, the supporting case 420 wasmanufactured in such a manner that the inner diameter of the supportingcase 420 was made almost the same as the diameter (330 mm) of the uppermetal plate 411, the heater 412 and the lower metal plate 411 are placedand fixedly secured inside the supporting case 420 with the side facesthereof being made in tightly contact with the supporting case 420;thus, a metal heater was manufactured.

COMPARATIVE EXAMPLE 1

A metal heater in which an intermediate plate made of copper and aheater were placed on the bottom face of a metal plate was manufactured.The thickness of the metal plate was 55 mm, and the pattern of theheating element was the same as that of Example 1.

A current was applied to each of the metal heaters according to Examples1 to 7, Test Examples 1 and 2 and Comparative Example 1 to raise thetemperature; thus, evaluation was made on each of the following points:(1) temperature evenness in surface in steady state, (2) temperatureevenness in surface in transition period, (3) measurements on flatness;(4) overshoot amount. The results thereof are shown in Table 1.

The respective evaluating processes were carried out by using thefollowing methods.

(1) Temperature Evenness in Surface in Steady State

After the temperature of the metal heater had been raised to 140° C., awafer with a temperature sensor equipped with a thermocouple was placedon the heating face of the metal heater so that the distribution oftemperature on the heating face was measured. The distribution oftemperature was indicated by a maximum value of a temperature differencebetween the highest temperature and the lowest temperature during thetemperature rise.

(2) Temperature Evenness in Surface in Transition Period

The wafer with a temperature sensor was heated from ordinary temperatureto 140° C. by the metal heater so that the distribution of temperaturein surface of the wafer with a temperature sensor was measured. Thedistribution of temperature was measured at 100° C., 120° C. and 130° C.respectively, and indicated by a maximum value of a temperaturedifference between the highest temperature and the lowest temperature.

(3) Measurements on Flatness

The flatness on the heating face of the metal plate was measured atordinary temperature as well as at 140° C. by a laser displacement gauge(made by Keyence Corporation).

(4) Overshoot Amount

The overshoot amount (the value obtained by subtracting the settemperature (140° C.) from the maximum temperature during the process)in the case where 20 silicon wafers were processed at 140° C. wasmeasured.

Here, with respect to the evaluation of (3) measurements on flatness, athree-dimensional shape of a part of the heating face of the metalheater according to Example 1 at ordinary temperature is shown in FIG.8; a three-dimensional shape of a part of the heating face of the metalheater according to Example 1 at 140° C. is shown in FIG. 9; and athree-dimensional shape of a part of the heating face of the metalheater according to Test Example 1 at 140° C. is shown in FIG. 10. TABLE1 Thickness of Distribution of Distribution of metal plate temperaturein temperature in Overshoot amount (mm) surface in surface in Flatness(μm) (° C.) Upper Lower steady state transition period At afterprocessing metal metal (° C.) (° C.) ordinary 20 wafers at plate plate140° C. 100° C. 120° C. 130° C. temperature 140° C. 140° C.) Example 115 5 0.17 5.37 2.38 2.01 29 30 0.30 Example 2 20 5 0.24 5.38 2.80 1.5129 30 0.35 Example 3 25 10 0.19 5.45 2.22 1.76 29 29 0.33 Example 4 40 50.25 4.80 2.24 1.64 28 29 0.31 Example 5 20 20 0.31 4.16 2.53 1.96 28 350.35 Example 6 36 3 0.32 4.20 2.53 1.95 28 36 0.30 Example 7 50 5 0.274.98 2.62 1.97 28 29 0.30 Test 5 20 0.44 9.56 6.66 5.10 37 47 1.32Example 1 Test 15 5 0.36 4.78 2.67 2.13 40 53 0.35 Example 2 Comparative55 0 0.42 5.58 3.66 2.36 44 56 0.32 Example 1As shown in Table 1, the metal heaters according to Examples 1 to 7 hadan even temperature on the heating face of the upper metal plate insteady state as well as in transition period. This is presumably becausethe thickness of the metal plate on the heating face side is large sothat heat transmitted to the metal plate is sufficiently dispersed toprevent the pattern of the heating element from being reflected to theheating face.

Moreover, as shown in Table 1 as well as in FIGS. 8 and 9, since theflatness in the metal heaters of Examples 1 to 4 is 50 μm or less, thedistance between the upper metal plate and the sensor wafer becomes lesslikely to have dispersion to provide an even heating process.

This is presumably because, since the metal heaters according toExamples 1 to 4 have a structure in which the lower metal plate having afixed thickness is placed on the bottom face of the heater, thermalradiation released from the heater is made even.

Furthermore, in the metal heaters of Examples 5 and 6, the temperatureevenness of the heating face in steady state is inferior to that of themetal heaters of Examples 1 to 4; however, the temperature evenness ofthe heating face in transition period is superior to that of the metalheaters of Examples 1 to 4.

In contrast, in the case of the metal heaters according to Test Examples1 and 2, the temperature of the heating face of the upper metal platewas uneven in steady state as well as in transition period. This ispresumably because the thickness of the upper metal plate is thin; thus,warping and sagging occur in the metal plate due to thermal expansionduring the heating process.

Moreover, in the metal heater according to Comparative Example 1, sincethe heater is placed on the bottom face of the metal plate without thelower metal plate, the flatness of the heating face becomes inferior;thus, the temperature on the heating face becomes uneven.

With respect to the overshoot amount, the measured results of the metalheater according to Test Example 1 gave values greater than those of themeasured results of the other metal heaters. This is presumably because,since the thickness of the lower metal plate is larger than thethickness of the upper metal plate with the thermal capacity of thelower metal plate being relatively greater than the thermal capacity ofthe upper metal plate, heat is accumulated in the lower metal plate tocause heat conduction from the lower metal plate to the upper metalplate and the subsequent overshooting phenomenon due to the heatconduction.

EXAMPLE 8

Manufacturing of Metal Heater (see FIG. 5)

(1) A plate-shaped member, made of an aluminum-copper alloy (A2219(JIS-H4000)), was machined at outer-diameter portion by using an NClathe (made by Washino Machinery Co., Ltd.) and formed into a diskshape, and this disk-shaped member was then subjected to an end-facemachining process, a surface machining process and a rear-face machiningprocess so that a disk-shaped member for an upper metal plate and adisk-shaped member for a lower metal plate were manufactured.

Next, each of parts to be through holes 515 to which lifter pins forsupporting a semiconductor wafer 519 are inserted, each of concaveportions in which supporting pins 518 are placed and a part to be abottomed hole 514 in which a temperature measuring element 516 isembedded were formed in these disk members by using a machining center(Hitachi Seiki Co., Ltd.).

Here, the through holes 515 were formed at three positions, and theconcave portions used for placing the supporting pins 518 were formed atnine positions.

After the bottomed holes or the through holes had been formed atpredetermined positions in the same manner, thread grooves were formedin the bottomed holes or the through holes so that screw holes throughwhich metal plate securing screws 517 are inserted were formed in thedisk members.

Here, the screw holes were formed in the upper metal plate and theplate-shaped member with a depth of ¾ of the thickness thereof.

(2) Next, the disk member for the upper metal plate, manufacturedthrough the processes of (1), was subjected to a surface grindingprocess on its surface on the heating face side by using a rotarygrinding machine (made by Okamoto Machine Tool Works, Ltd.) so that anupper metal plate 511 having a thickness of 15 mm and a diameter of 330mm and a lower metal plate 521 having a thickness of 5 mm and a diameterof 330 mm were obtained.

Moreover, a barrier ring for a wafer that is an object to be heated wasformed on the side face of the upper metal plate 511 by using thefollowing method.

In other words, the outer rim portion of the supporting case was madehigher than the upper face of the heating face of the upper metal plateso that the barrier ring 532 was formed.

Here, in this example, the thickness of the upper metal plate 511 wasmade larger than the thickness of the lower metal plate 521.

(3) Next, the upper metal plate 511 and the lower metal plate 521 weresubjected to an alumite treatment under conditions of 10% H₂SO₄electrolytic solution, a voltage of 10 V, a current density of 0.8 A/dm²and a liquid temperature of 20° C. so that an oxide coat film having athickness of 15 μm was formed on each of the surfaces of the upper metalplate 511 and the lower metal plate 521.

(4) A heating element, made of a stainless foil having a thickness of200 μm on which a winding wire is placed in a repeated pattern to form aring shape and a winding wire is repeatedly placed in a pattern so as toform a part of each of concentric circles as shown in FIG. 2, wassandwiched between two mica plates having a thickness of 0.3 mm toobtain a heater 512 having a diameter of 330 mm.

Here, in the heater 512, the heating element was formed so that theouter rim of the heating element was placed at a position within 25% ofthe diameter of the upper metal plate 511 from the periphery of theupper metal plate 511, and the total number of the circuits of theheating element was set to four.

Moreover, parts to be through holes 515, a part to be the bottomed hole514 and parts to be screw holes through which metal plate securingscrews 517 are inserted were preliminary formed in the mica plate 526.

Thereafter, the heater 512 was sandwiched between the upper metal plate511 and the lower metal plate 521 manufactured through the processes of(1) to (3), and after the metal plate securing screws 517 had beeninserted through the screw holes formed in the lower metal plate 521 andthe heater 512, the securing screws were tightened so that the uppermetal plate 511, the lower metal plate 521 and the heater 512 werecombined into an integral part.

(5) Next, a supporting case 520 having a cylinder shape with a bottom asshown in FIG. 5, made of SUS, was manufactured, and a supporting plate525 was placed on the bottom face of the supporting case 520 and partsto be the through holes 515, a part to be the bottomed hole 514 and athrough hole through which the conductive wire 524 was inserted had beenformed in the bottom face of the supporting case 520, a heat shieldingplate 523 having a disk shape, made of SUS, was placed on the bottomportion of the supporting case 520.

Moreover, the upper metal plate 511 to which the heater 512 and thelower metal plate 521 had been attached, manufactured in the process(4), was placed inside the supporting case 520 on which the heatshielding plate 523 had been placed through the supporting plate 525,and fixedly secured therein.

(6) After a temperature measuring element 516 made of a platinumtemperature measuring resistor for use in controlling temperatures hadbeen inserted into the bottomed hole 514, the bottomed hole 514 wassealed by using an inorganic bonding agent (Aron ceramic, made byToagosei Co., Ltd.) serving as a sealing material. Moreover, supportingpins 518 were placed in the concave portions formed on the heating faceof the upper metal plate 511.

(7) Next, the conductive wire 524 was wrapped by a connecting stainlessfoil 530 taken out of the stainless foil 529 serving as the heatingelement attached to the heater 512, and this was then caulked with anattaching member 531 attached thereto so that the conductive wire 524was attached to the connecting stainless foil 530, and connected to anexternal power supply or the like; thus, a metal heater 510 wasobtained.

EXAMPLE 9

Manufacturing of Metal Heater

The same processes as those of Example 8 were carried out except thatthe thickness of the upper metal plate 511 was set to 20 mm and that thethickness of the lower metal plate 521 was set to 5 mm so that a metalheater was manufactured.

EXAMPLE 10

Manufacturing of Metal Heater

The same processes as those of Example 8 were carried out except thatthe thickness of the upper metal plate 511 was set to 25 mm and that thethickness of the lower metal plate 521 was set to 10 mm so that a metalheater was manufactured.

EXAMPLE 11

Manufacturing of Metal Heater

The same processes as those of Example 8 were carried out except thatthe thickness of the upper metal plate 511 was set to 40 mm and that thethickness of the lower metal plate 521 was set to 5 mm so that a metalheater was manufactured.

TEST EXAMPLE 3

The same processes as those of Example 8 were carried out except thatthe lower metal plate was made of copper so that a metal heater wasmanufactured. In this test example, the thickness of the upper metalplate was made larger than the thickness of the lower metal plate.

A current was applied to each of the metal heaters according to Examples8 to 11 and Test Example 3 to raise the temperature; thus, evaluationwas made on each of the following points: (1) temperature evenness insurface in steady state, (2) temperature evenness in surface intransition period, (3) measurements on flatness; (4) overshoot amount.The results thereof are shown in Table 2. Here, the same evaluationmethod as the method of Example 1 was used.

Moreover, in the evaluation of the measurements on the flatness (5), athree dimensional shape of a part of a metal heater heating face ofExample 8 at ordinary temperature is shown in FIG. 11, a threedimensional shape of a part of a metal heater heating face of Example 8at 140° C. is shown in FIG. 12, and a three dimensional shape of a partof a metal heater heating face of Test Example 3 at 140° C. is shown inFIG. 13. TABLE 2 Thickness of Distribution of Distribution of metalplate temperature in temperature in Overshoot amount (mm) surface insurface in Flatness (μm) (° C.) Upper Lower steady state transitionperiod At after processing metal metal (° C.) (° C.) ordinary 20 wafersat plate plate 140° C. 100° C. 120° C. 130° C. temperature 140° C. 140°C.) Example 8 15 5 0.17 5.37 2.38 1.62 29 30 0.31 Example 9 20 5 0.245.38 2.80 1.51 29 30 0.34 Example 10 25 10 0.19 5.45 2.22 1.76 29 290.32 Example 11 40 5 0.25 4.80 2.24 1.64 28 29 0.35 Test 20 5 0.52 4.483.33 1.86 28 40 0.30 Example 3 Comparative 55 0 0.42 5.58 3.66 2.36 4456 0.32 Example 1

As shown in Table 2, the metal heaters according to Examples 8 to 11 hadan even temperature on the heating face of the upper metal plate insteady state as well as in transition period. This is presumablybecause, since the material of the metal plate on the heating face sideas well as on the opposite side was the same, the thermal expansioncoefficient was equal so that no warping occurs even upon a temperaturerise; thus, no dispersion occurs in the distance between the wafer andthe heating face, making it possible to carry out an even heatingprocess.

In contrast, in the case of the metal heater according to Test Example3, since the materials of the upper metal plate and the lower metalplate are different from each other, the thermal expansion coefficientsare different from each other, with the result that a deformation occursupon heating to cause dispersion in the temperature of the heating face.

Moreover, the metal heaters according to Examples 8 to 11 have superiortemperature evenness on the heating face in steady state as well as intransition period, in comparison with the metal heater according to theabove-mentioned Comparative Example 1.

With respect to the overshoot amount, all the metal heaters according toExamples 8 to 11, Test Example 3 and Comparative Example 1 had almostthe same measured results.

EXAMPLE 12

Manufacturing of Metal Heater (see FIGS. 6(a) and 6(b), and FIG. 7)

(1) A plate-shaped member, made of an aluminum-copper alloy (A2219(JIS-H4000)), was machined at outer diameter portion by using an NClathe (made by Washino Machinery Co., Ltd.) and formed into a diskshape, and this disk-shaped member was then subjected to an end-facemachining process, a surface machining process and a rear-face machiningprocess so that a disk-shaped member for an upper metal plate and adisk-shaped member for a lower metal plate were manufactured.

Next, each of parts to be through holes 615 to which lifter pins usedfor supporting a semiconductor wafer 619 are inserted, each of parts tobe concave portions 628 in which supporting pins 618 are placed and apart to be a bottomed hole 614 in which a temperature measuring element616 is embedded were formed in this disk-shaped member by using amachining center (Hitachi Seiki Co., Ltd.).

Here, the through holes 615 were formed at three positions, and theconcave portions used for placing the supporting pins 618 were formed atnine positions. With respect to the layout of the positions, as shown inFIG. 6(a), eight supporting pins were placed on circumferences ofconcentric circles of the upper metal plate with equal intervals, and asingle supporting pin was placed in the center portion of the uppermetal plate.

After the bottomed holes or the through holes had been formed atpredetermined positions in the same manner, thread grooves were formedin the bottomed holes or the through holes so that screw holes throughwhich metal plate securing screws 617 are inserted were formed in thedisk member.

Here, the screw holes were formed in the upper metal plate and theplate-shaped member with a depth of ¾ of the thickness thereof.

(2) Next, the disk member for the upper metal plate, manufacturedthrough the processes of (1), was subjected to a surface grindingprocess on its surface on the heating face side by using a rotarygrinding machine (manufactured by Okamoto Machine Tool Works, Ltd.) sothat an upper metal plate 611 having a thickness of 15 mm and a diameterof 330 mm and a lower metal plate 621 having a thickness of 5 mm and adiameter of 330 mm were obtained.

Moreover, a barrier ring for a wafer that is an object to be heated wasformed on the side face of the upper metal plate 611 by using thefollowing method. In other words, the outer rim portion of thesupporting case was made higher than the upper face of the heating faceof the upper metal plate so that the barrier ring 632 was formed.

Here, in this example, the thickness of the upper metal plate 611 wasmade larger than the thickness of the lower metal plate 621.

(3) Next, the upper metal plate 611 and the lower metal plate 621 weresubjected to an alumite treatment under conditions of 10% H₂SO₄electrolytic solution, a voltage of 10 V, a current density of 0.8 A/dm²and a liquid temperature of 20° C. so that an oxide coat film having athickness of 15 μm was formed on each of the surfaces of the upper metalplate 611 and the lower metal plate 621.

(4) A heating element, made of a stainless foil having a thickness of200 μm on which, as shown in FIG. 7, a winding wire is repeatedly placedin a repeated pattern to form a ring shape and a winding wire isrepeatedly placed in a pattern so as to form a part of each ofconcentric circles, was sandwiched between two mica plates having athickness of 0.3 mm to obtain a heater 612 having a diameter of 330 mm.

Here, in the heater 612, the heating element was formed so that the areaincluding the heating element had a diameter of 320 mm, and the totalnumber of the circuits of the heating element was set to four.

Moreover, parts to be through holes 615, a part to be the bottomed hole614 and parts to be screw holes through which metal plate securingscrews 617 are inserted were preliminary formed in the mica plate 626.

Thereafter, the heater 612 was sandwiched between the upper metal plate611 and the lower metal plate 621 manufactured through the processes of(1) to (3), and after the metal plate securing screws 617 had beeninserted through the screw holes provided in the lower metal plate 621and the heater 612, the securing screws were tightened so that the uppermetal plate 611, the lower metal plate 621 and the heater 612 werecombined into an integral part.

(5) Next, a supporting case 620 having a cylinder shape with a bottom asshown in FIG. 6(a), made of SUS, was manufactured, and a supportingplate 625 was placed on the bottom face of this supporting case 620;then, after parts to be the through holes 615, apart to be the bottomedhole 614 and a through hole through which the conductive wire 624 isinserted had been formed in the bottom face of the supporting case 620,a heat shielding plate 623 having a cylinder shape, made of SUS, wasplaced on the bottom portion of the supporting case 620.

Moreover, the upper metal plate 611 to which the heater 612 and thelower metal plate 621 had been attached, manufactured in (4), was placedinside the supporting case 620 in which the heat shielding plate 623 hadbeen placed, and fixedly secured therein through the supporting plate625.

(6) After a Pt temperature measuring element 616 made of a Pttemperature measuring resistor for use in controlling temperatures hadbeen inserted into the bottomed hole 614, the bottomed hole 614 wassealed by using an inorganic bonding agent (Aron ceramic, made byToagosei Co., Ltd.). Moreover, supporting pins 618 having a shape asshown in FIG. 6(a), made of alumina, were inserted into nine concaveportions 628 formed on the heating face of the upper metal plate 611,and a spring 627 having a C-shape was fitted to each concave portion 628in a manner so as to surround each supporting pin 618 so that thesupporting pins were fixedly secured onto the heating face 611 a of theupper metal plate 611.

(7) Next, the conductive wire 624 was wrapped by a connecting stainlessfoil 630 taken out of a stainless foil 629 serving as the heatingelement provided in the heater 612, and an attaching member 631 wasattached thereto, and this was then caulked so that the conductive wire624 was attached to the connecting stainless foil 630, and connected toan external power supply or the like; thus, a metal heater 610 wasobtained.

EXAMPLE 13

Manufacturing of Metal Heater

The same processes as those of Example 12 were carried out except thatthe thickness of the upper metal plate 611 was set to 20 mm and that thethickness of the lower metal plate 621 was set to 5 mm, with the numberof pins set to six in total, one in the center and five on the samecircumference on the periphery thereof, so that a metal heater wasmanufactured.

EXAMPLE 14

Manufacturing of Metal Heater

The same processes as those of Example 12 were carried out except thatthe thickness of the upper metal plate 611 was set to 25 mm and that thethickness of the lower metal plate 621 was set to 10 mm, with the numberof pins set to nineteen in total, one in the center, six on the samecircumference on the periphery thereof, and twelve on the samecircumference located outside thereof, so that a metal heater wasmanufactured.

EXAMPLE 15

Manufacturing of Metal Heater

The same processes as those of Example 12 were carried out except thatthe thickness of the upper metal plate 611 was set to 40 mm and that thethickness of the lower metal plate 621 was set to 5 mm so that a metalheater was manufactured.

EXAMPLE 16

The same processes as those of Example 12 were carried out except thatin the process (2) of Example 12, five concave portions for placingsupporting pins were formed on the surface on the heating face side ofthe circular plate member for the upper metal plate and that in theprocess (6) thereof, supporting pins were placed in the five concaveportions formed on the heating face of the upper metal plate so that ametal heater was manufactured. In Example 16, total five supporting pinswere placed on the heating face of the upper metal plate with a layoutin which four supporting pins were placed on circumferences ofconcentric circles of the upper metal plate with equal intervals, with asingle supporting pin placed in the center of the upper metal plate.

EXAMPLE 17

In this example, the same processes as those of Example 12 were carriedout except that the heater had a diameter of 220 mm, and that the numberof pins was set to five in total, that is, one in the center and four onthe same circumference on the periphery thereof; thus, a metal heaterwas manufactured.

EXAMPLE 18

In this example, the same processes as those of Example 12 were carriedout except that the heater had a diameter of 220 mm, and that the numberof pins was set to fifteen in total, that is, one in the center, four onthe same circumference on the periphery thereof and ten on the samecircumference outside thereof; thus, a metal heater was manufactured.

TEST EXAMPLE 4

In this test example, the same processes as those of Example 12 werecarried out except that the number of pins was set to four in total,that is, one in the center and three on the same circumference on theperiphery thereof so that a metal heater was manufactured.

TEST EXAMPLE 5

In this test example, the same processes as those of Example 17 werecarried out except that three supporting pins were placed oncircumferences of concentric circles of the upper metal plate with equalintervals so that a metal heater was manufactured.

COMPARATIVE EXAMPLE 2

A metal heater in which an intermediate plate made of copper and aheater were placed on the bottom face of a metal plate was manufactured.The thickness of the metal plate was 55 mm, and the pattern of theheating element was the same as that of Example 12, without anysupporting pins.

A current was applied to each of the metal heaters according to Examples12 to 18, Test Examples 4 and5and Comparative Example 2 to raise thetemperature; thus, evaluation was made on each of the following points:(1) temperature evenness in surface in steady state, (2) temperatureevenness in surface in transition period, (3) measurements on flatness;(4) overshoot amount. The results thereof are shown in Table 3. Here,the same evaluation method as that of Example 1 was used.

Here, with respect to the evaluation of (2) temperature evenness insurface in transition period, the relationship between the temperatureand time at each of measuring points of the wafer with a temperaturesensor, obtained when measurements are carried out by using the metalheater according to Example 12, is shown in each of FIGS. 14 to 16, andthe relationship between the temperature and time at each of measuringpoints of the wafer with a temperature sensor, obtained whenmeasurements are carried out by using the metal heater according toExample 16, is shown in each of FIGS. 17 to 19.

FIGS. 14 and 17 show the relationship between the temperature and timein the vicinity of 100° C.; FIGS. 15 and 18 show the relationshipbetween the temperature and time in the vicinity of 120 to 130° C.; andFIGS. 16 and 19 show the relationship between the temperature and timein the vicinity of 140° C.

Moreover, with respect to (3) measurements on flatness, athree-dimensional shape of a part of the heating face of the metalheater according to Example 12 at ordinary temperature is shown in FIG.20; a three-dimensional shape of a part of the heating face of the metalheater according to Example 12 at 140° C. is shown in FIG. 21; and athree-dimensional shape of a part of the heating face of the metalheater according to Comparative Example 2 at 140° C. is shown in FIG.22. TABLE 3 Thickness of Distribution of Distribution of metal platetemperature in temperature in Overshoot amount (mm) surface in surfacein Flatness (μm) (° C.) Upper Lower steady state transition period Atafter processing metal metal (° C.) (° C.) ordinary 20 wafers at plateplate 140° C. 100° C. 120° C. 130° C. temperature 140° C. 140° C.Example 12 15 5 0.17 5.37 2.38 2.01 29 30 0.30 Example 13 20 5 0.24 5.382.80 1.51 29 30 0.33 Example 14 25 10 0.19 5.45 2.22 1.76 29 29 0.32Example 15 40 5 0.25 4.80 2.24 1.64 28 29 0.35 Example 16 15 5 0.3817.30 12.19 7.53 29 30 0.31 Example 17 15 15 0.18 5.31 2.30 2.00 29 300.34 Example 18 15 15 0.19 5.20 2.75 1.86 29 30 0.33 Test 15 5 0.2511.90 8.20 5.20 30 33 0.30 Example 4 Test 15 15 0.29 12.67 10.00 5.75 2930 0.35 Example 5 Comparative 55 0 1.31 20.00 15.30 9.38 44 56 0.34Example 2

As shown in Table 3 as well as in FIGS. 14 to 16, the metal heatersaccording to Examples 12 to 15 had an even temperature on the heatingface of the upper metal plate in steady state as well as in transitionperiod. This is presumably because, since the thickness of the metalplate on the heating face side is higher than a certain value, heat,transmitted through the metal plate, is sufficiently dispersed so thatthe pattern of the heating element is not reflected to the heating face.

Moreover, the fact that the temperature is maintained in an even level,in particular, in transition period is because, since the intervalbetween the supporting pins is narrow, no sagging occurs in the sensorwafer so that no dispersion occurs in the distance between the heatingface of the upper metal plate and the sensor wafer.

Since the metal heaters according to examples 12 to 15 are allowed tohave a flatness of 50 μm or less, as shown in Table 3 as well as inFIGS. 20 and 21, no dispersion occurs in the distance between the uppermetal plate and the sensor wafer, making it possible to carry out aneven heating process.

Furthermore, in the metal heaters according to examples 12 to 15, sincethe lower metal plate having a certain thickness is placed on the bottomface of the heater, thermal radiation released from the heater is madeeven.

In contrast, in the case of the metal heater according to Example 16, intransition period, the temperature on the heating face of the uppermetal plate became uneven as shown in Table 3 and FIGS. 17 to 19. Thereason that dispersion occur in the temperature of the heating face isbecause, since the interval between the supporting pins is wider, slightsagging occurs in the sensor wafer, with the result that slightdispersion occur in the distance between the heating face of the uppermetal plate and the sensor wafer. In this case, however, the temperatureon the heating face of the upper metal plate is maintained in an almosteven level in steady state, causing no serious problems in practicaluse.

Moreover, in the metal heaters according to Examples 17 and 18, as shownin Table 3, the temperature on the heating face of the upper metal plateis maintained in an even level in steady state as well as in transitionperiod. This is presumably because, since a sufficient number ofsupporting pins are arranged on the heating face, the clearance betweenthe heating face and the semiconductor wafer is precisely maintainedwithout any sagging in the semiconductor wafer; thus, it becomespossible to easily ensure the evenness in the temperature of the heatingface, in particular, the evenness in the temperature of the heating facein transition period.

As shown in Table 3, in the case of the metal heater according to TestExample 4, the temperature on the heating face of the upper metal platebecomes uneven in transition period, in comparison with the metal heateraccording to Example 12. Moreover, in the case of the metal heateraccording to Test Example 5, as shown in Table 3, the temperature on theheating face of the upper metal plate becomes uneven in transitionperiod, in comparison with the metal heater according to Example 17. Thereason that dispersion occur in the temperature on the heating face intransition period is because, since the interval between the supportingpins is wide, slight sagging occurs in the sensor wafer to cause slightdispersion in the distance between the heating face of the upper metalplate and the sensor wafer.

As shown in Table 3, in the case of the metal heater according toComparative Example 2, the temperature on the heating face of the uppermetal plate is uneven in steady state as well as in transition period.The reason that dispersion occur in the temperature on the heating faceis presumably because big undulation occurs to cause dispersion in thedistance between the metal plate and the sensor wafer.

With respect to the overshoot amount, all the measured results of themetal heaters according to Examples 8 to 11, Test Example 3 andComparative Example 1 are almost the same.

INDUSTRIAL APPLICABILITY

As described above, the metal heater according to the first aspect ofthe present invention makes it possible to more quickly heat an objectto be heated, such as a semiconductor wafer or the like, in comparisonwith a metal heater that is formed by a single metal plate with a heaterplaced on the side opposite to the heating face side of the metal plate.

Moreover, since the metal heater according to the first aspect of thepresent invention is designed so that the thickness of the metal plateon the heating face side is the same as, or larger than the thickness ofa metal plate on the side opposite to the heating face side, theflatness of the heating face is improved at the time of heating, and thetemperature evenness is also improved so that it becomes possible toevenly heat the entire semiconductor wafer.

As described above, the metal heater according to the second aspect ofthe present invention makes it possible to more quickly heat an objectto be heated, such as a semiconductor wafer or the like, in comparisonwith a metal heater that is formed by a single metal plate with a heaterplaced on the side opposite to the heating face side of the metal plate.

Moreover, since the metal heater according to the second aspect of thepresent invention is designed so that a plurality of metal platesconstituting the metal heater are made from the same material, theflatness of the heating face is improved at the time of heating, and thedistance between the semiconductor wafer and the object to be heated canbe made constant so that it becomes possible to heat the semiconductorwafer or the like evenly.

As described above, the metal heater according to the third aspect ofthe present invention makes it possible to more quickly heat an objectto be heated, such as a semiconductor wafer or the like, in comparisonwith a metal heater that is formed by a single metal plate with a heaterplaced on the side opposite to the heating face side of the metal plate.

Moreover, since the metal heater according to the third aspect of thepresent invention is designed so that a convex portion for supporting anobject to be heated is placed on the heating face opposing the object tobe heated of the metal plate corresponding to an area on which a heatingelement is formed, it is possible to make a semiconductor wafer or thelike, that is, the object to be heated, less likely to generate sagging;thus, the distance between the semiconductor wafer or the like and theheating face of the metal plate can be made constant so that it becomespossible to heat the semiconductor wafer or the like evenly.

1. A metal heater comprising a metal plate and a heating element,wherein the number of said metal plates is a plural number, said heatingelement is sandwiched between said metal plates, and the thickness of ametal plate on a heating face side is the same as or larger than thethickness of a metal plate on a side opposite to said heating face side.2. The metal heater according to claim 1, wherein said heating elementis divided into two or more portions.
 3. A metal heater comprising aplurality of metal plates and a heating element, said heating elementsandwiched between said metal plates, wherein said plurality of metalplates are made of the same material.
 4. The metal heater according toclaim 3, wherein said plurality of metal plates comprises acopper-aluminum alloy.
 5. A metal heater comprising a plurality of metalplates and a heating element, with said heating element sandwichedbetween said metal plates, wherein a convex portion for supporting anobject to be heated is placed on a heating face opposing the object tobe heated, of said metal plate corresponding to an area on which saidheating element is formed.
 6. The metal heater according to claim 5,wherein the area on which said heating element is formed has a diameterof 250 mm or more, and the number of convex portions is 6 or more. 7.The metal heater according to claim 5, wherein the area on which saidheating element is formed has a diameter of 200 to 250 mm, and thenumber of said convex portions is 5 or more.
 8. The metal heateraccording to any of claims 5 to 7, wherein said heating element isdivided into two or more portions.